A Houthi militant checks documents loaded on a van destroyed by Saudi-air strikes on the offices of the education ministry's workers union in Yemen's northwestern city of Amran August 19, 2015. A Saudi-led Arab coalition has been bombarding the Iranian-allied Houthi rebel movement - Yemen's dominant force - since late March in a bid to reinstate exiled President Abd-Rabbu Mansour Hadi, who has fled to Riyadh. REUTERS/Khaled Abdullah 

Posters of Yemen's former president Ali Abdullah Saleh are seen on the wall of a room in a house destroyed by Saudi-led air strikes on the nearby offices of the education ministry's workers union in Yemen's northwestern city of Amran August 19, 2015. A Saudi-led Arab coalition has been bombarding the Iranian-allied Houthi rebel movement - Yemen's dominant force - since late March in a bid to reinstate exiled President Abd-Rabbu Mansour Hadi, who has fled to Riyadh. REUTERS/Khaled Abdullah 

A Houthi militant holds a fragment of a missile as he searches the rubble of the offices of the education ministry's workers union, destroyed by Saudi-led air strikes, in Yemen's northwestern city of Amran August 19, 2015. A Saudi-led Arab coalition has been bombarding the Iranian-allied Houthi rebel movement - Yemen's dominant force - since late March in a bid to reinstate exiled President Abd-Rabbu Mansour Hadi, who has fled to Riyadh. REUTERS/Khaled Abdullah 

People check the wreckage of cars destroyed by Saudi-led air strikes on the nearby offices of the education ministry's workers union in Yemen's northwestern city of Amran August 19, 2015. A Saudi-led Arab coalition has been bombarding the Iranian-allied Houthi rebel movement - Yemen's dominant force - since late March in a bid to reinstate exiled President Abd-Rabbu Mansour Hadi, who has fled to Riyadh. REUTERS/Khaled Abdullah TPX IMAGES OF THE DAY

A Houthi militant pushes the wheelchair of an injured comrade past the offices of the education ministry's workers union, destroyed by Saudi-led air strikes, in Yemen's northwestern city of Amran August 19, 2015. A Saudi-led Arab coalition has been bombarding the Iranian-allied Houthi rebel movement - Yemen's dominant force - since late March in a bid to reinstate exiled President Abd-Rabbu Mansour Hadi, who has fled to Riyadh. REUTERS/Khaled Abdullah 

A Houthi militant reacts in front the offices of the education ministry's workers union, destroyed by Saudi-led air strikes, in Yemen's northwestern city of Amran August 19, 2015. A Saudi-led Arab coalition has been bombarding the Iranian-allied Houthi rebel movement - Yemen's dominant force - since late March in a bid to reinstate exiled President Abd-Rabbu Mansour Hadi, who has fled to Riyadh. REUTERS/Khaled Abdullah 

Houthi militants walk on the rubble of the offices of the education ministry's workers union, destroyed by Saudi-led air strikes, in Yemen's northwestern city of Amran August 19, 2015. A Saudi-led Arab coalition has been bombarding the Iranian-allied Houthi rebel movement - Yemen's dominant force - since late March in a bid to reinstate exiled President Abd-Rabbu Mansour Hadi, who has fled to Riyadh. REUTERS/Khaled Abdullah TPX IMAGES OF THE DAY

People ride atop a car on a road linking Yemen's capital Sanaa with the northwestern city of Amran July 27, 2015. Fuel shortages in Yemen have caused hikes in taxi fees, forcing many to ride on overcrowded vehicles. REUTERS/Khaled Abdullah 

People ride on the back of a truck on a road linking Yemen's capital Sanaa with the northwestern city of Amran July 27, 2015. Fuel shortages in Yemen have caused hikes in taxi fees, forcing many to ride in overcrowded vehicles. REUTERS/Khaled Abdullah TPX IMAGES OF THE DAY 

Engineers stand on a fuel storage tank damaged by a recent Saudi-led air strike at a cement factory in Yemen's northwestern city of Amran July 27, 2015. Yemen's Houthi group carried on fighting across Yemen on Monday despite a ceasefire announcement by its Saudi-led foes, and media controlled by the Iran-allied movement acknowledged that its forces had shelled targets inside Saudi Arabia. REUTERS/Khaled Abdullah 

Engineers look at damage caused by a recent Saudi-led air strike, in a cement factory in Yemen's northwestern city of Amran July 27, 2015. Yemen's Houthi group carried on fighting across Yemen on Monday despite a ceasefire announcement by its Saudi-led foes, and media controlled by the Iran-allied movement acknowledged that its forces had shelled targets inside Saudi Arabia. REUTERS/Khaled Abdullah 

A Houthi militant looks at damage inside the hall of a government compound, hit by recent Saudi-led air strikes, in Yemen's northwestern city of Amran July 27, 2015. Yemen's Houthi group carried on fighting across Yemen on Monday despite a ceasefire announcement by its Saudi-led foes, and media controlled by the Iran-allied movement acknowledged that its forces had shelled targets inside Saudi Arabia. REUTERS/Khaled Abdullah 

Engineers stand on a fuel storage tank damaged by a recent Saudi-led air strike, in a cement factory in Yemen's northwestern city of Amran July 27, 2015. Yemen's Houthi group carried on fighting across Yemen on Monday despite a ceasefire announcement by its Saudi-led foes, and media controlled by the Iran-allied movement acknowledged that its forces had shelled targets inside Saudi Arabia. REUTERS/Khaled Abdullah 

A Houthi militant looks on as he walks inside a government compound, destroyed by recent Saudi-led air strikes, in Yemen's northwestern city of Amran July 27, 2015. Yemen's Houthi group carried on fighting across Yemen on Monday despite a ceasefire announcement by its Saudi-led foes, and media controlled by the Iran-allied movement acknowledged that its forces had shelled targets inside Saudi Arabia. REUTERS/Khaled Abdullah 

A part of a window frame is seen in front of government compound, destroyed by recent Saudi-led air strikes, in Yemen's northwestern city of Amran July 27, 2015. Yemen's Houthi group carried on fighting across Yemen on Monday despite a ceasefire announcement by its Saudi-led foes, and media controlled by the Iran-allied movement acknowledged that its forces had shelled targets inside Saudi Arabia. REUTERS/Khaled Abdullah 

A Houthi militant walks in front of a government compound, destroyed by recent Saudi-led air strikes, in Yemen's northwestern city of Amran July 27, 2015. Yemen's Houthi group carried on fighting across Yemen on Monday despite a ceasefire announcement by its Saudi-led foes, and media controlled by the Iran-allied movement acknowledged that its forces had shelled targets inside Saudi Arabia. REUTERS/Khaled Abdullah 

A Houthi militant walks in front of a government compound, destroyed by recent Saudi-led air strikes, in Yemen's northwestern city of Amran July 27, 2015. Yemen's Houthi group carried on fighting across Yemen on Monday despite a ceasefire announcement by its Saudi-led foes, and media controlled by the Iran-allied movement acknowledged that its forces had shelled targets inside Saudi Arabia. REUTERS/Khaled Abdullah TPX IMAGES OF THE DAY

An internally displaced woman washes dishes as she sits in a cave in the district of Khamir of Yemen's northwestern province of Amran May 9, 2015. Internally displaced Yemenis were forced to leave their homes in the nearby province of Saada amid Saudi-led air strikes. REUTERS/Mohamed al-Sayaghi 

An internally displaced woman sits with a child in a cave in the district of Khamir of Yemen's northwestern province of Amran May 9, 2015. Internally displaced Yemenis were forced to leave their homes in the nearby province of Saada amid Saudi-led air strikes. REUTERS/Mohamed al-Sayaghi 

An internally displaced woman sits with a child in a cave in the district of Khamir of Yemen's northwestern province of Amran May 9, 2015. Internally displaced Yemenis were forced to leave their homes in the nearby province of Saada amid Saudi-led air strikes. REUTERS/Mohamed al-Sayaghi 

An internally displaced girl stands in a cavein the district of Khamir of Yemen's northwestern province of Amran May 9, 2015. Internally displaced Yemenis were forced to leave their homes in the nearby province of Saada amid Saudi-led air strikes. REUTERS/Mohamed al-Sayaghi 

An internally displaced man sits in a cave in the district of Khamir of Yemen's northwestern province of Amran May 9, 2015. Internally displaced Yemenis were forced to leave their homes in the nearby province of Saada amid Saudi-led air strikes. REUTERS/Mohamed al-Sayaghi 

Internally displaced children transport water with a cart in the district of Khamir of Yemen's northwestern province of Amran May 9, 2015. Internally displaced Yemenis were forced to leave their homes in the nearby province of Saada amid Saudi-led air strikes. REUTERS/Mohamed al-Sayaghi 

An internally displaced girl carries water on her head in the district of Khamir of Yemen's northwestern province of Amran May 9, 2015. Internally displaced Yemenis were forced to leave their homes in the nearby province of Saada amid Saudi-led air strikes. REUTERS/Mohamed al-Sayaghi 

Internally displaced people ride on the back of a truck as they flee in the district of Khamir of Yemen's northwestern province of Amran May 9, 2015. They were forced to leave their homes in the nearby province of Saada amid Saudi-led air strikes. REUTERS/Mohamed al-Sayaghi 

Internally displaced people ride on the back of a truck as they flee in the district of Khamir of Yemen's northwestern province of Amran May 9, 2015. They were forced to leave their homes in the nearby province of Saada amid Saudi-led air strikes. REUTERS/Mohamed al-Sayaghi 

Internally displaced people ride on the back of a truck as they flee in the district of Khamir of Yemen's northwestern province of Amran May 9, 2015. They were forced to leave their homes in the nearby province of Saada amid Saudi-led air strikes. REUTERS/Mohamed al-Sayaghi 

Internally displaced people ride on the back of a truck as they flee in the district of Khamir of Yemen's northwestern province of Amran May 9, 2015. They were forced to leave their homes in the nearby province of Saada amid Saudi-led air strikes. REUTERS/Mohamed al-Sayaghi 

Internally displaced people fill water in a school in the district of Khamir of Yemen's northwestern province of Amran May 9, 2015. They were forced to leave their homes in the nearby province of Saada amid Saudi-led air strikes. REUTERS/Mohamed al-Sayaghi 

A boy eats with other internally displaced people in a school in the district of Khamir of Yemen's northwestern province of Amran May 9, 2015. They were forced to leave their homes in the nearby province of Saada amid Saudi-led air strikes. REUTERS/Mohamed al-Sayaghi 

Internally displaced people fill water in a school in the district of Khamir of Yemen's northwestern province of Amran May 9, 2015. They were forced to leave their homes in the nearby province of Saada amid Saudi-led air strikes. REUTERS/Mohamed al-Sayaghi 

Internally displaced people receive bedding in a school in the district of Khamir of Yemen's northwestern province of Amran May 9, 2015. They were forced to leave their homes in the nearby province of Saada amid Saudi-led air strikes. REUTERS/Mohamed al-Sayaghi 

A boy eats with other internally displaced people in a school in the district of Khamir of Yemen's northwestern province of Amran May 9, 2015. They were forced to leave their homes in the nearby province of Saada amid Saudi-led air strikes. REUTERS/Mohamed al-Sayaghi 

Internally displaced people stand in a school in the district of Khamir of Yemen's northwestern province of Amran May 9, 2015. They were forced to leave their homes in the nearby province of Saada amid Saudi-led air strikes. REUTERS/Mohamed al-Sayaghi 

Internally displaced people receive bedding in a school in the district of Khamir of Yemen's northwestern province of Amran May 9, 2015. They were forced to leave their homes in the nearby province of Saada amid Saudi-led air strikes. REUTERS/Mohamed al-Sayaghi 

Internally displaced people receive bedding in a school in the district of Khamir of Yemen's northwestern province of Amran May 9, 2015. They were forced to leave their homes in the nearby province of Saada amid Saudi-led air strikes. REUTERS/Mohamed al-Sayaghi 

Internally displaced people receive bedding in a school in the district of Khamir of Yemen's northwestern province of Amran May 9, 2015. They were forced to leave their homes in the nearby province of Saada amid Saudi-led air strikes. REUTERS/Mohamed al-Sayaghi 

People inspect the rubble of a house, destroyed by an air strike, in Amran province, northwest of Yemen's capital Sanaa April 12, 2015. REUTERS/Khaled Abdullah 

People inspect the rubble of a house, destroyed by an air strike, in Amran province, northwest of Yemen's capital Sanaa April 12, 2015. REUTERS/Khaled Abdullah 

People gather around a crater cause by an air strike in Amran province, northwest of Yemen's capital Sanaa April 12, 2015. REUTERS/Khaled Abdullah 

People inspect the rubble of a house, destroyed by an air strike, in Amran province, northwest of Yemen's capital Sanaa April 12, 2015. REUTERS/Khaled Abdullah 

People stand on the rubble of a house, destroyed by an air strike, in Amran province, northwest of Yemen's capital Sanaa April 12, 2015. REUTERS/Khaled Abdullah 

People stand on the rubble of a house, destroyed by an air strike, in Amran province, northwest of Yemen's capital Sanaa April 12, 2015. REUTERS/Khaled Abdullah 

Boys stand on the rubble of a house, destroyed by an air strike, in Amran province, northwest of Yemen's capital Sanaa April 12, 2015. REUTERS/Khaled Abdullah 

A man walks past the rubble of a house, destroyed by an air strike, in Amran province, northwest of Yemen's capital Sanaa April 12, 2015. REUTERS/Khaled Abdullah 

People stand on the rubble of a house, destroyed by an air strike, in Amran province, northwest of Yemen's capital Sanaa April 12, 2015. REUTERS/Khaled Abdullah 

People gather at the site of an air strike in Amran province, northwest of Yemen's capital Sanaa April 12, 2015. REUTERS/Khaled Abdullah 

People stand on the rubble of a house, destroyed by an air strike, in Amran province, northwest of Yemen's capital Sanaa April 12, 2015. REUTERS/Khaled Abdullah 

People walk on the rubble of a house, destroyed by an air strike, in Amran province, northwest of Yemen's capital Sanaa April 12, 2015. REUTERS/Khaled Abdullah 

People look at the rubble of a house, destroyed by an air strike, in Amran province, northwest of Yemen's capital Sanaa April 12, 2015. REUTERS/Khaled Abdullah 

People stand on the rubble of a house, destroyed by an air strike, in Amran province, northwest of Yemen's capital Sanaa April 12, 2015. REUTERS/Khaled Abdullah 

People gather at the site of an air strike in Amran province, northwest of Yemen's capital Sanaa April 12, 2015. REUTERS/Khaled Abdullah 

People gather at the site of an air strike in Amran province, northwest of Yemen's capital Sanaa April 12, 2015. REUTERS/Khaled Abdullah 

People gather at the site of an air strike in Amran province, northwest of Yemen's capital Sanaa April 12, 2015. REUTERS/Khaled Abdullah 

People gather at the site of an air strike in Amran province, northwest of Yemen's capital Sanaa April 12, 2015. REUTERS/Khaled Abdullah 

People gather at the site of an air strike in Amran province, northwest of Yemen's capital Sanaa April 12, 2015. REUTERS/Khaled Abdullah 

Tribesmen perform the traditional Baraa dance during a celebration marking the Eid al-Adha in a rural area of Yemen's north-western province of Amran October 5, 2014. REUTERS/Khaled Abdullah (YEMEN - Tags: SOCIETY RELIGION) 

Tribesmen chant traditional songs during a celebration marking Eid al-Adha in a rural area of the northwestern Yemeni province of Amran October 5, 2014. REUTERS/Khaled Abdullah (YEMEN - Tags: SOCIETY RELIGION) 

Tribesmen chant traditional songs during a celebration marking Eid al-Adha in a rural area of the northwestern Yemeni province of Amran October 5, 2014. REUTERS/Khaled Abdullah (YEMEN - Tags: SOCIETY RELIGION) 

Children gather to watch a celebration marking Eid al-Adha in a rural area of the northwestern Yemeni province of Amran October 5, 2014. REUTERS/Khaled Abdullah (YEMEN - Tags: SOCIETY RELIGION)