Airport police patrol a passenger concourse as a policeman (L) retrieves a suspicious package at Ronald Reagan National Airport, Arlington, Virginia, U.S., November 7, 2016. REUTERS/Mike Theiler

Airport police retrieve a suspicious package at Ronald Reagan National Airport, Arlington, Virginia, U.S., November 7, 2016. The day before the U.S. presidential elections there is heightened security due to an unspecified terrorist threat from Al Qaeda. REUTERS/Mike Theiler

An airport policeman (L) awaits a K-9 unit to check out a suspicious package at Ronald Reagan National Airport, Arlington, Virginia, U.S., November 7, 2016. The day before the U.S. presidential elections there is heightened security due to an unspecified terrorist threat from Al Qaeda. REUTERS/Mike Theiler

Airport police check out a suspicious package at Ronald Reagan National Airport, Arlington, Virginia, U.S., November 7, 2016. The day before the U.S. presidential elections there is heightened security due to an unspecified terrorist threat from Al Qaeda. REUTERS/Mike Theiler

A security guard stands on the step to the House of Representatives at the U.S. Capitol in Washington, U.S., November 7, 2016. REUTERS/Joshua Roberts

A security camera hangs near the U.S. Capitol in Washington, U.S., November 7, 2016. REUTERS/Joshua Roberts

A workman repairs a security camera near the White House in Washington, U.S., November 7, 2016. REUTERS/Joshua Roberts

A rebel fighter from Jaysh al-Sunna, operating under a coalition of rebel groups called Jaish al-Fatah, or the army of conquest, rests in Aziziyah village, southern Aleppo countryside, Syria May 17, 2016. To match Insight MIDEAST-CRISIS/SYRIA-ALQAEDA REUTERS/Khalil Ashawi

A rebel fighter from Jaysh al-Sunna, operating under a coalition of rebel groups called Jaish al-Fatah, or the army of conquest, rests in Aziziyah village, southern Aleppo countryside, Syria May 17, 2016. To match Insight MIDEAST-CRISIS/SYRIA-ALQAEDA REUTERS/Khalil Ashawi TPX IMAGES OF THE DAY

A rebel fighter from Jaysh al-Sunna, operating under a coalition of rebel groups called Jaish al-Fatah, or the army of conquest, sits in front of a map of Aleppo's countryside in Aziziyah village, southern Aleppo countryside, Syria May 17, 2016. To match Insight MIDEAST-CRISIS/SYRIA-ALQAEDA REUTERS/Khalil Ashawi

A rebel fighter from Jaysh al-Sunna, operating under a coalition of rebel groups called Jaish al-Fatah, or the army of conquest, prepares his weapon as others rest in Aziziyah village, southern Aleppo countryside, Syria May 17, 2016. To match Insight MIDEAST-CRISIS/SYRIA-ALQAEDA REUTERS/Khalil Ashawi

A rebel fighter from Jaysh al-Sunna, operating under a coalition of rebel groups called Jaish al-Fatah, or the army of conquest, rests in Aziziyah village, southern Aleppo countryside, Syria May 17, 2016. To match Insight MIDEAST-CRISIS/SYRIA-ALQAEDA REUTERS/Khalil Ashawi

Rebel fighters from Jaysh al-Sunna, operating under a coalition of rebel groups called Jaish al-Fatah, or the army of conquest, gather inside a building at a lookout point in Aziziyah village, southern Aleppo countryside, Syria May 17, 2016. To match Insight MIDEAST-CRISIS/SYRIA-ALQAEDA REUTERS/Khalil Ashawi

Rebel fighters from Jaysh al-Sunna, operating under a coalition of rebel groups called Jaish al-Fatah, or the army of conquest, rest in Aziziyah village, southern Aleppo countryside, Syria May 17, 2016. To match Insight MIDEAST-CRISIS/SYRIA-ALQAEDA REUTERS/Khalil Ashawi TPX IMAGES OF THE DAY

Tribesmen attend a tribal gathering to show support to authorities against al Qaeda militants in their areas in the Arhab region north of the Yemeni capital Sanaa May 29, 2014. Yemen's security forces on Sunday killed a senior al Qaeda leader wanted for attacks on local and foreign targets in Sanaa, the Yemeni government said, after a raid in Arhab in which at least four other militants died. REUTERS/Khaled Abdullah (YEMEN - Tags: POLITICS SOCIETY CIVIL UNREST)

Tribesmen attend a tribal gathering to show support to authorities against al Qaeda militants in their areas in the Arhab region north of the Yemeni capital Sanaa May 29, 2014. Yemen's security forces on Sunday killed a senior al Qaeda leader wanted for attacks on local and foreign targets in Sanaa, the Yemeni government said, after a raid in Arhab in which at least four other militants died. REUTERS/Khaled Abdullah (YEMEN - Tags: POLITICS SOCIETY CIVIL UNREST)

Tribesmen attend a tribal gathering to show support to authorities against al Qaeda militants in their areas in the Arhab region, north of the Yemeni capital Sanaa May 29, 2014. Yemen's security forces on Sunday killed a senior al Qaeda leader wanted for attacks on local and foreign targets in Sanaa, the Yemeni government said, after a raid in Arhab in which at least four other militants died. REUTERS/Khaled Abdullah (YEMEN - Tags: POLITICS SOCIETY CIVIL UNREST)

Tribesmen attend a tribal gathering held following a police raid on a hideout of al Qaeda militants in the Arhab region, north of the Yemeni capital Sanaa May 27, 2014. Yemen's security forces on Sunday killed a senior al Qaeda leader wanted for attacks on local and foreign targets in Sanaa, the Yemeni government said, after the raid in which at least four other militants died. REUTERS/Khaled Abdullah (YEMEN - Tags: POLITICS CIVIL UNREST)

A woman carries her daughter at their family's flat damaged during a police raid on a nearby hideout of al Qaeda militants in the Arhab region north of the Yemeni capital Sanaa May 27, 2014. Yemen's security forces on Sunday killed a senior al Qaeda leader wanted for attacks on local and foreign targets in Sanaa, the Yemeni government said, after the raid in which at least four other militants died. REUTERS/Khaled Abdullah (YEMEN - Tags: POLITICS CIVIL UNREST)

A girl is seen in her family's flat damaged during a police raid on a nearby hideout of al Qaeda militants in the Arhab region north of the Yemeni capital Sanaa May 27, 2014. Yemen's security forces on Sunday killed a senior al Qaeda leader wanted for attacks on local and foreign targets in Sanaa, the Yemeni government said, after the raid in which at least four other militants died. REUTERS/Khaled Abdullah (YEMEN - Tags: POLITICS CIVIL UNREST)

People look at damage caused by a police raid on a hideout of al Qaeda militants in the Arhab region north of the Yemeni capital Sanaa May 27, 2014. Yemen's security forces on Sunday killed a senior al Qaeda leader wanted for attacks on local and foreign targets in Sanaa, the Yemeni government said, after the raid in which at least four other militants died. REUTERS/Khaled Abdullah (YEMEN - Tags: POLITICS CIVIL UNREST)

People look at damage caused by a police raid on a hideout of al Qaeda militants in the Arhab region north of the Yemeni capital Sanaa May 27, 2014. Yemen's security forces on Sunday killed a senior al Qaeda leader wanted for attacks on local and foreign targets in Sanaa, the Yemeni government said, after the raid in which at least four other militants died. REUTERS/Khaled Abdullah (YEMEN - Tags: POLITICS CIVIL UNREST)

People look at damage caused by a police raid on a hideout of al Qaeda militants in the Arhab region north of the Yemeni capital Sanaa May 27, 2014. Yemen's security forces on Sunday killed a senior al Qaeda leader wanted for attacks on local and foreign targets in Sanaa, the Yemeni government said, after the raid in which at least four other militants died. REUTERS/Khaled Abdullah (YEMEN - Tags: POLITICS CIVIL UNREST)

Boys look at a vehicle destroyed during a police raid on a hideout of al Qaeda militants in the Arhab region, north of the Yemeni capital Sanaa May 27, 2014. Yemen's security forces on Sunday killed a senior al Qaeda leader wanted for attacks on local and foreign targets in Sanaa, the Yemeni government said, after the raid in which at least four other militants died. REUTERS/Khaled Abdullah (YEMEN - Tags: POLITICS CIVIL UNREST)

People walk by a damaged wall caused by a police raid on a hideout of al Qaeda militants in the Arhab region north of the Yemeni capital Sanaa May 27, 2014. Yemen's security forces on Sunday killed a senior al Qaeda leader wanted for attacks on local and foreign targets in Sanaa, the Yemeni government said, after the raid in which at least four other militants died. REUTERS/Khaled Abdullah (YEMEN - Tags: POLITICS CIVIL UNREST)

Boys look at a vehicle destroyed during a police raid on a hideout of al Qaeda militants in the Arhab region, north of the Yemeni capital Sanaa May 27, 2014. Yemen's security forces on Sunday killed a senior al Qaeda leader wanted for attacks on local and foreign targets in Sanaa, the Yemeni government said, after the raid in which at least four other militants died. REUTERS/Khaled Abdullah (YEMEN - Tags: POLITICS CIVIL UNREST TPX IMAGES OF THE DAY)

Boys look at a vehicle destroyed during a police raid on a hideout of al Qaeda militants in the Arhab region, north of the Yemeni capital Sanaa May 27, 2014. Yemen's security forces on Sunday killed a senior al Qaeda leader wanted for attacks on local and foreign targets in Sanaa, the Yemeni government said, after the raid in which at least four other militants died. REUTERS/Khaled Abdullah (YEMEN - Tags: POLITICS CIVIL UNREST)

People look at damages caused by a police raid on a hideout of al Qaeda militants in the Arhab region, north of the Yemeni capital Sanaa May 27, 2014. Yemen's security forces on Sunday killed a senior al Qaeda leader wanted for attacks on local and foreign targets in Sanaa, the Yemeni government said, after the raid in which at least four other militants died. REUTERS/Khaled Abdullah (YEMEN - Tags: POLITICS CIVIL UNREST)

People look at a vehicle destroyed during a police raid on a hideout of al Qaeda militants in the Arhab region, north of the Yemeni capital Sanaa May 27, 2014. Yemen's security forces on Sunday killed a senior al Qaeda leader wanted for attacks on local and foreign targets in Sanaa, the Yemeni government said, after the raid in which at least four other militants died. REUTERS/Khaled Abdullah (YEMEN - Tags: POLITICS CIVIL UNREST)

Boys stand outside a house, damaged during a police raid, in the Arhab region, north of the Yemeni capital Sanaa May 27, 2014. Yemen's security forces on Sunday killed a senior al Qaeda leader wanted for attacks on local and foreign targets in Sanaa, the Yemeni government said, after the raid in which at least four other militants died. REUTERS/Khaled Abdullah (YEMEN - Tags: POLITICS CIVIL UNREST)

IRAQ-VIOLENCE/AL QAEDA - Map showing al Qaeda's presence in western Iraq, where the group is seeking to establish an "Islamic state". (SIN01)

A police trooper mans a machine gun mounted on a police truck securing the vicinity of the Defence Ministry compound in Sanaa December 7, 2013. Yemen said on Friday it had regained full control of its Defence Ministry compound in Sanaa a day after a militant attack, claimed by an al Qaeda-affiliated group, killed 56 people, including foreign medical staff. REUTERS/Khaled Abdullah (YEMEN - Tags: MILITARY POLITICS CIVIL UNREST)

Police troopers inspect cars at a checkpoint near the Defence Ministry compound in Sanaa December 7, 2013. Yemen said on Friday it had regained full control of its Defence Ministry compound in Sanaa a day after a militant attack, claimed by an al Qaeda-affiliated group, killed 56 people, including foreign medical staff. REUTERS/Khaled Abdullah (YEMEN - Tags: MILITARY POLITICS CIVIL UNREST)

Police troopers inspect cars at a checkpoint near the Defence Ministry compound in Sanaa December 7, 2013. Yemen said on Friday it had regained full control of its Defence Ministry compound in Sanaa a day after a militant attack, claimed by an al Qaeda-affiliated group, killed 56 people, including foreign medical staff. REUTERS/Khaled Abdullah (YEMEN - Tags: MILITARY POLITICS CIVIL UNREST)

Police troopers inspect cars at a checkpoint near the Defence Ministry compound in Sanaa December 7, 2013. Yemen said on Friday it had regained full control of its Defence Ministry compound in Sanaa a day after a militant attack, claimed by an al Qaeda-affiliated group, killed 56 people, including foreign medical staff. REUTERS/Khaled Abdullah (YEMEN - Tags: MILITARY POLITICS CIVIL UNREST)

A police trooper stands guard at a checkpoint near the Defence Ministry compound in Sanaa December 7, 2013. Yemen said on Friday it had regained full control of its Defence Ministry compound in Sanaa a day after a militant attack, claimed by an al Qaeda-affiliated group, killed 56 people, including foreign medical staff. REUTERS/Khaled Abdullah (YEMEN - Tags: MILITARY POLITICS CIVIL UNREST)

A police trooper mans a machine gun mounted on a police truck securing the vicinity of the Defence Ministry compound in Sanaa December 7, 2013. Yemen said on Friday it had regained full control of its Defence Ministry compound in Sanaa a day after a militant attack, claimed by an al Qaeda-affiliated group, killed 56 people, including foreign medical staff. REUTERS/Khaled Abdullah (YEMEN - Tags: MILITARY POLITICS CIVIL UNREST)

A police trooper stands guard at a checkpoint near the Defence Ministry compound in Sanaa December 7, 2013. Yemen said on Friday it had regained full control of its Defence Ministry compound in Sanaa a day after a militant attack, claimed by an al Qaeda-affiliated group, killed 56 people, including foreign medical staff. REUTERS/Khaled Abdullah (YEMEN - Tags: MILITARY POLITICS CIVIL UNREST)

People walk past a police trooper standing guard at a checkpoint near the Defence Ministry compound in Sanaa December 7, 2013. Yemen said on Friday it had regained full control of its Defence Ministry compound in Sanaa a day after a militant attack, claimed by an al Qaeda-affiliated group, killed 56 people, including foreign medical staff. REUTERS/Khaled Abdullah (YEMEN - Tags: MILITARY POLITICS CIVIL UNREST)

Police troopers stand guard on a police truck securing the vicinity of the Defence Ministry compound in Sanaa December 7, 2013. Yemen said on Friday it had regained full control of its Defence Ministry compound in Sanaa a day after a militant attack, claimed by an al Qaeda-affiliated group, killed 56 people, including foreign medical staff. REUTERS/Khaled Abdullah (YEMEN - Tags: MILITARY POLITICS CIVIL UNREST)

A police officer stops cars on the road leading to the Defence Ministry in Sanaa December 6, 2013. An al Qaeda-linked group has claimed responsibility for Thursday's attack on Yemen's defence ministry that killed at least 52 people, the country's worst militant assault in 18 months. REUTERS/Mohamed al-Sayaghi (YEMEN - Tags: POLITICS CIVIL UNREST MILITARY TRANSPORT)

A police officer stops a car on the road leading to the Defence Ministry in Sanaa December 6, 2013. An al Qaeda-linked group has claimed responsibility for Thursday's attack on Yemen's defence ministry that killed at least 52 people, the country's worst militant assault in 18 months. REUTERS/Mohamed al-Sayaghi (YEMEN - Tags: POLITICS CIVIL UNREST MILITARY TRANSPORT)

Police officers stop a motorcyclist on the road leading to the Defence Ministry in Sanaa December 6, 2013. An al Qaeda-linked group has claimed responsibility for Thursday's attack on Yemen's defence ministry that killed at least 52 people, the country's worst militant assault in 18 months. REUTERS/Mohamed al-Sayaghi (YEMEN - Tags: CIVIL UNREST POLITICS MILITARY TRANSPORT)

A fire engine drives past the Defence Ministry compound in Sanaa December 6, 2013. An al Qaeda-linked group has claimed responsibility for Thursday's attack on Yemen's defence ministry that killed at least 52 people, the country's worst militant assault in 18 months. REUTERS/Mohamed al-Sayaghi (YEMEN - Tags: POLITICS MILITARY CIVIL UNREST)

People carry the bodies of Abdul Jalil Mohammed Noman Noman and his wife Asma Ali Mohamed Noman, two of the victims of a bombing at the Ministry of Defence compound during a funeral in Sanaa December 6, 2013. An al Qaeda-linked group has claimed responsibility for Thursday's attack on Yemen's defence ministry that killed at least 52 people, the country's worst militant assault in 18 months. REUTERS/Mohamed al-Sayaghi (YEMEN - Tags: CIVIL UNREST POLITICS MILITARY)

People carry the bodies of Abdul Jalil Mohammed Noman Noman and his wife Asma Ali Mohamed Noman, two of the victims of a bombing at the Ministry of Defence compound during a funeral in Sanaa December 6, 2013. An al Qaeda-linked group has claimed responsibility for Thursday's attack on Yemen's defence ministry that killed at least 52 people, the country's worst militant assault in 18 months. REUTERS/Mohamed al-Sayaghi (YEMEN - Tags: MILITARY POLITICS CIVIL UNREST)

Relatives hug during the funeral of Abdul Jalil Mohammed Noman Noman and his wife Asma Ali Mohamed Noman, two of the victims of a bombing at the Ministry of Defence compound in Sanaa December 6, 2013. An al Qaeda-linked group has claimed responsibility for Thursday's attack on Yemen's defence ministry that killed at least 52 people, the country's worst militant assault in 18 months. REUTERS/Mohamed al-Sayaghi (YEMEN - Tags: CIVIL UNREST POLITICS MILITARY)

People carry the bodies of Abdul Jalil Mohammed Noman Noman and his wife Asma Ali Mohamed Noman two of the victims of a bombing of the Ministry of Defence compound during a funeral in Sanaa December 6, 2013. An al Qaeda-linked group has claimed responsibility for Thursday's attack on Yemen's defence ministry that killed at least 52 people, the country's worst militant assault in 18 months. REUTERS/Mohamed al-Sayaghi (YEMEN - Tags: CIVIL UNREST POLITICS MILITARY)

Yemen's Health Minister Ahmad al-Ansi listens to an army officer, injured in an attack on the Defence Ministry's compound, at a hospital in Sanaa December 6, 2013. An al Qaeda-linked group has claimed responsibility for Thursday's attack on Yemen's defence ministry that killed at least 52 people, the country's worst militant assault in 18 months. REUTERS/Khaled Abdullah (YEMEN - Tags: HEALTH POLITICS CIVIL UNREST MILITARY)

Yemen's Health Minister Ahmad al-Ansi (L) checks on an army officer, injured in an attack on the Defence Ministry's compound, at a hospital in Sanaa December 6, 2013. An al Qaeda-linked group has claimed responsibility for Thursday's attack on Yemen's defence ministry that killed at least 52 people, the country's worst militant assault in 18 months. REUTERS/Khaled Abdullah (YEMEN - Tags: HEALTH POLITICS CIVIL UNREST MILITARY)

A nurse tends to an army officer, injured in an attack on the Defence Ministry's compound, at a hospital in Sanaa December 6, 2013. An al Qaeda-linked group has claimed responsibility for Thursday's attack on Yemen's defence ministry that killed at least 52 people, the country's worst militant assault in 18 months. REUTERS/Khaled Abdullah (YEMEN - Tags: HEALTH POLITICS CIVIL UNREST MILITARY)

Nurses tend to an army officer, injured in an attack on the Defence Ministry's compound, at a hospital in Sanaa December 6, 2013. An al Qaeda-linked group has claimed responsibility for Thursday's attack on Yemen's defence ministry that killed at least 52 people, the country's worst militant assault in 18 months. REUTERS/Khaled Abdullah (YEMEN - Tags: HEALTH POLITICS CIVIL UNREST MILITARY)

Relatives of an army officer, injured in an attack on the Defence Ministry's compound, help him at a hospital in Sanaa December 6, 2013. An al Qaeda-linked group has claimed responsibility for Thursday's attack on Yemen's defence ministry that killed at least 52 people, the country's worst militant assault in 18 months. REUTERS/Khaled Abdullah (YEMEN - Tags: HEALTH POLITICS CIVIL UNREST MILITARY)

ALQAEDA-NETWORK/ - Map showing al Qaeda's affiliates and areas of operation

- IRAQ-VIOLENCE/ALQAEDA - Map showing Iraq's ethnic-religious areas and hotspots where al Qaeda has captured towns and villages. (SIN07)

Royal Canadian Mounted Police Assistant Commissioner Wayne Rideout displays a picture of pressure cookers used by two individuals arrested while conspiring to commit a terrorist attack in Surrey, British Columbia July 2, 2013. The two people took steps to build explosive devices and planned to place them at the British Columbia Legislature in Victoria. REUTERS/Andy Clark (CANADA - Tags: CRIME LAW)

Spain's Interior Minister Jorge Fernandez Diaz (R) talks to aides after a news conference at the ministry headquarters in Madrid August 2, 2012. Diaz said police arrested on Wednesday two al Qaeda members from ex-Soviet republics close to Ciudad Real who were likely heading to France, and a Turkish man near Cadiz whose house was searched and where explosives were found. REUTERS/Susana Vera (SPAIN - Tags: POLITICS CRIME LAW)

Spain's Interior Minister Jorge Fernandez Diaz listens to a question during a news conference at the ministry headquarters in Madrid August 2, 2012. Diaz said police arrested on Wednesday two al Qaeda members from ex-Soviet republics close to Ciudad Real who were likely heading to France, and a Turkish man near Cadiz whose house was searched and where explosives were found. REUTERS/Susana Vera (SPAIN - Tags: POLITICS CRIME LAW)

Spain's Interior Minister Jorge Fernandez Diaz gestures as he listens to a question during a news conference at the ministry headquarters in Madrid August 2, 2012. Diaz said police arrested on Wednesday two al Qaeda members from ex-Soviet republics close to Ciudad Real who were likely heading to France, and a Turkish man near Cadiz whose house was searched and where explosives were found. REUTERS/Susana Vera (SPAIN - Tags: POLITICS CRIME LAW)

Spain's Interior Minister Jorge Fernandez Diaz gestures as he answers a question during a news conference at the ministry headquarters in Madrid August 2, 2012. Diaz said police arrested on Wednesday two al Qaeda members from ex-Soviet republics close to Ciudad Real who were likely heading to France, and a Turkish man near Cadiz whose house was searched and where explosives were found. REUTERS/Susana Vera (SPAIN - Tags: POLITICS CRIME LAW)