Afghan police arrive at the site of an attack in Kabul June 10, 2013. Explosions were heard by Reuters witnesses and there were reports of gunfire near Afghanistan's main international airport in the capital, Kabul, early on Monday, and a police spokesman said insurgents had launched the attack. REUTERS/Omar Sobhani (AFGHANISTAN - Tags: CIVIL UNREST TPX IMAGES OF THE DAY)

Smoke billows from the site of an explosion in Kabul June 10, 2013. Insurgents launched a pre-dawn attack on Afghanistan's main international airport in the capital, Kabul, on Monday, police said, with explosions and gunfire heard coming from an area that also houses major foreign military bases. There were no immediate reports of casualties and there was also no early claim of responsibility for the attack. REUTERS/Omar Sobhani (AFGHANISTAN - Tags: CIVIL UNREST)

Afghan security forces arrive at the site of an attack in Kabul June 10, 2013. Insurgents launched the pre-dawn attack on Afghanistan's main international airport in the capital, Kabul, on Monday, police said, with explosions and gunfire heard coming from an area that also houses major foreign military bases. There were no immediate reports of casualties and there was also no early claim of responsibility for the attack. REUTERS/Omar Sobhani (AFGHANISTAN - Tags: CIVIL UNREST)

A NATO soldier takes his position near the site of an attack in Kabul June 10, 2013. Insurgents launched the pre-dawn attack on Afghanistan's main international airport in the capital, Kabul, on Monday, police said, with explosions and gunfire heard coming from an area that also houses major foreign military bases. There were no immediate reports of casualties and there was also no early claim of responsibility for the attack. REUTERS/Omar Sobhani (AFGHANISTAN - Tags: CIVIL UNREST MILITARY)

Afghan security forces arrive at the site of an attack in Kabul June 10, 2013. Insurgents launched the pre-dawn attack on Afghanistan's main international airport in the capital, Kabul, on Monday, police said, with explosions and gunfire heard coming from an area that also houses major foreign military bases. There were no immediate reports of casualties and there was also no early claim of responsibility for the attack. REUTERS/Omar Sobhani (AFGHANISTAN - Tags: CIVIL UNREST)

A member of the Afghan security forces walks towards the site of an attack in Kabul June 10, 2013. Insurgents launched the pre-dawn attack on Afghanistan's main international airport in the capital, Kabul, on Monday, police said, with explosions and gunfire heard coming from an area that also houses major foreign military bases. There were no immediate reports of casualties and there was also no early claim of responsibility for the attack. REUTERS/Omar Sobhani (AFGHANISTAN - Tags: CIVIL UNREST TPX IMAGES OF THE DAY)

Afghan police arrive at the site of an attack in Kabul June 10, 2013. Explosions were heard by Reuters witnesses and there were reports of gunfire near Afghanistan's main international airport in the capital, Kabul, early on Monday, and a police spokesman said insurgents had launched the attack. REUTERS/Omar Sobhani (AFGHANISTAN - Tags: CIVIL UNREST)

Afghans gather near the site of an attack in Kabul June 10, 2013. Insurgents launched the pre-dawn attack on Afghanistan's main international airport in the capital, Kabul, on Monday, police said, with explosions and gunfire heard coming from an area that also houses major foreign military bases. There were no immediate reports of casualties and there was also no early claim of responsibility for the attack. REUTERS/Omar Sobhani (AFGHANISTAN - Tags: CIVIL UNREST)

Smoke billows from the site of an attack at the main international airport in Kabul June 10, 2013. Insurgents launched the pre-dawn attack on Afghanistan's main international airport in the capital, Kabul, on Monday, police said, with explosions and gunfire heard coming from an area that also houses major foreign military bases. There were no immediate reports of casualties and there was also no early claim of responsibility for the attack. REUTERS/Omar Sobhani (AFGHANISTAN - Tags: CIVIL UNREST)

Afghan police arrive at the site of an attack in Kabul June 10, 2013. Insurgents launched the pre-dawn attack on Afghanistan's main international airport in the capital, Kabul, on Monday, police said, with explosions and gunfire heard coming from an area that also houses major foreign military bases. There were no immediate reports of casualties and there was also no early claim of responsibility for the attack. REUTERS/Omar Sobhani (AFGHANISTAN - Tags: CIVIL UNREST)

Afghan security forces take their position at the site of an attack in Kabul June 10, 2013. Insurgents launched the pre-dawn attack on Afghanistan's main international airport in the capital, Kabul, on Monday, police said, with explosions and gunfire heard coming from an area that also houses major foreign military bases. There were no immediate reports of casualties and there was also no early claim of responsibility for the attack. REUTERS/Omar Sobhani (AFGHANISTAN - Tags: CIVIL UNREST)

Afghan security forces arrive at the site of an attack in Kabul June 10, 2013. Insurgents launched the pre-dawn attack on Afghanistan's main international airport in the capital, Kabul, on Monday, police said, with explosions and gunfire heard coming from an area that also houses major foreign military bases. There were no immediate reports of casualties and there was also no early claim of responsibility for the attack. REUTERS/Omar Sobhani (AFGHANISTAN - Tags: CIVIL UNREST)

Smoke billows from the site of an explosion in Kabul June 10, 2013. Insurgents launched a pre-dawn attack on Afghanistan's main international airport in the capital, Kabul, on Monday, police said, with explosions and gunfire heard coming from an area that also houses major foreign military bases. There were no immediate reports of casualties and there was also no early claim of responsibility for the attack. REUTERS/Omar Sobhani (AFGHANISTAN - Tags: CIVIL UNREST)

Afghan security forces arrive at the site of an attack in Kabul June 10, 2013. Insurgents launched the pre-dawn attack on Afghanistan's main international airport in the capital, Kabul, on Monday, police said, with explosions and gunfire heard coming from an area that also houses major foreign military bases. There were no immediate reports of casualties and there was also no early claim of responsibility for the attack. REUTERS/Omar Sobhani (AFGHANISTAN - Tags: CIVIL UNREST)