A picture taken on November 16, 2015 shows a Saudi pilot sitting in a F-15 fighter jet at the Khamis Mushayt military airbase, some 880 km from Riyadh, as the Saudi army conducts operations over Yemen. #

Armed Yemeni tribesmen from the Popular Resistance Committees, supporting forces loyal to Yemen's Saudi-backed President Abedrabbo Mansour Hadi, fire from a tank in the area of Sirwah, west of Marib city, on November 3, 2015. #

A Yemeni Shiite Houthi rebel stands next to a national flag in the capital Sanaa on September 21, 2015, during a ceremony marking a year since the city's seizure. #

A dog walks on the rubble of a house after an air strike in Sanaa on December 29, 2015. The air strike, carried out by Saudi forces, hit a neighborhood here, killing four people and injuring four more. #

Armed Yemeni tribesmen from the Popular Resistance Committees, supporting forces loyal to Yemen's Saudi-backed President Abedrabbo Mansour Hadi, fire as they hold a position in the area of Sirwah, west of Marib city, on December 18, 2015. #

A Yemeni soldier, pictured through a vehicle's windscreen, which was damaged by a bullet, gestures out of the window, in Marib, Yemen, on October 15, 2015. Marib is a city that is heavily armed even by the standards of Yemen, where the ready availability of weapons helped start civil war and is now preventing anyone coming out on top. Yemenis often say there are three guns for every person, a boast that has become an urgent concern in a country where the United Nations says the humanitarian situation is "critical". #

Firefighters attempt to extinguish a fire at a foodstuff storage facility destroyed by a Saudi-led air strike in Yemen's Red Sea port city of Houdieda on January 6, 2016. #

Yemeni artist Murad Subai installs a graffiti project on a wall protesting a Saudi-led blockade imposed on Yemen, in Sanaa, on December 31, 2015. Saudi Arabia has imposed a blockade on the impoverished nation since March 2015, as part of its ongoing campaign against the Houthis. #

A soldier loyal to Yemen's government stands on the back of a truck transporting landmines left by the Houthi rebels in al-Jadaan area, which was taken by pro-government army from the Houthis, in the country's central province of Marib, on December 21, 2015. #

The feet of a child covered in dust are seen as people search for survivors under the rubble of a house destroyed by an air strike at the old quarter of Yemen's capital Sanaa on September 19, 2015. At least ten Yemeni civilians were killed in air strikes by Saudi-led warplanes that targeted this neighborhood, medical sources said. #

An Emirati gunner watches for enemy fire from the rear gate of a United Arab Emirates Chinook military helicopter flying over Yemen on September 17, 2015. The Saudi-led coalition targeting Yemen's Shiite rebels pounded the insurgents' positions with heavy artillery fire on the outskirts of the central city of Marib, part of their push to retake the capital, Sanaa. #

Yemeni President Abed Rabbo Mansour Hadi, center, walks with officials as he tours in the port of Aden, Yemen, on January 4, 2016. Yemen's government declared a nighttime curfew in Aden in a bid to push back against recent incursions by al-Qaida and other Islamic militant groups, the city's governor said. #

People gather at the site of a car bomb attack that killed the governor of the port city of Aden on December 6, 2015. Jaafar Mohammed Saad was killed on Sunday when a suicide bomber rammed his car into the governor's convoy in the western part of Aden city, residents and a local official said. #

People walk past headgear lying on the ground at the al-Balili mosque after two bombings at the mosque in Sanaa on September 24, 2015. Two suicide bombers blew themselves up at a mosque run by Yemen's Houthi group in the capital Sanaa on the first day of the Muslim Eid al-Adha holiday, causing many casualties, witnesses said. #

People carry a man injured from clashes between tribal fighters and Houthis in Taiz, Yemen on October 21, 2015. Shiite Houthi rebels fired mortars and rockets into the central city of Taiz, killing at least 17 civilians and wounding over 70, including women, children, and the elderly, officials said. #

A man stands on a poster of Yemeni President Abed Rabbo Mansour Hadi among the wreckage of a municipal building destroyed by a Saudi-led air strike in Yemen's capital Sanaa, on January 3, 2016. #