In this Monday, April 20, 2015 file photo, a Shiite fighter known as Houthi checks an item on a street littered by debris after a Saudi-led airstrike hit a site where many believe the largest weapons cache in Yemen's capital, Sanaa, is located. (Photo by Hani Mohammed/AP Photo)

Shiite rebels known as Houthis hold up their weapons to denounce the Saudi-led airstrikes as they chant slogans during a protest in Sanaa, Yemen, Monday, April 27, 2015. Saudi-led airstrikes on Monday targeted Shiite rebels across Yemen, killing several people in the southern port city of Aden and striking a weapons depot in the rebel-held capital, officials and witnesses said. (Photo by Hani Mohammed/AP Photo)

In this Sunday, April 26, 2015 photo, men on a motorbike rush a man who was injured during a crossfire between tribal fighters and Shiite militia known as Houthis, to a hospital, in Taiz, Yemen. The fighting in Taiz between government forces and rebels was heaviest around government and security buildings in the city center, killing some 20 civilians and wounding dozens more, they said, adding that indiscriminately fired mortar rounds hit several private residences and landed near a hospital at one point. (Photo by Abdulnasser Alseddik/AP Photo)

A boy looks at the bloodstains on a vehicle which was used to transport victims near the rubble of houses destroyed by an air strike in the Okash village near Sanaa, April 4, 2015. (Photo by Mohamed al-Sayaghi/Reuters)

Children ride on the back of a pick-up truck with their luggage as they flee Saudi-led air strikes in Sanaa, April 6, 2015. (Photo by Khaled Abdullah/Reuters)

A boy pulls containers of water after he filled them at a faucet, amid an acute shortage of clean drinking water in Sanaa, April 20, 2015. (Photo by Mohamed al-Sayaghi/Reuters)

A worker throws a stuffed toy to another as they move furniture from a house damaged after an air strike by a Saudi-led coalition struck a nearby missile base, in Yemen's capital Sanaa, April 23, 2015. (Photo by Khaled Abdullah/Reuters)

A girl sits inside her house which was damaged by a shell which landed from a nearby missile base after the base was struck by a Saudi-led coalition air strike, near Sanaa, April 23, 2015. (Photo by Mohamed al-Sayaghi/Reuters)

A woman cries after her home was damaged by a shell which landed from a nearby missile base after the base was struck by a Saudi-led coalition air strike, near Sanaa, April 23, 2015. (Photo by Mohamed al-Sayaghi/Reuters)

A girl carries jerrycans she filled with water from a public tap amid an acute shortage of water supplies to houses in Sanaa April 26, 2015. (Photo by Khaled Abdullah/Reuters)

A woman carries a jerrycan she filled with water from a public tap amid an acute shortage of water supplies to houses in Sanaa April 26, 2015. (Photo by Khaled Abdullah/Reuters)

Girls carry jerrycans they filled with water from a public tap amid an acute shortage of water supply to houses in Sanaa April 26, 2015. (Photo by Khaled Abdullah/Reuters)

Women carry jerrycans they filled with water from a public tap amid an acute shortage of water supply to houses in Sanaa April 26, 2015. (Photo by Khaled Abdullah/Reuters)

A man rides a motorcycle past a headquarters of the Houthi group, which was destroyed after an air strike by a Saudi-led coalition, in Yemen's northwestern city of Saada April 26, 2015. (Photo by Reuters/Stringer)

People stand by the body of a tribal fighter killed in fighting against Houthi militia in Taiz April 26, 2015. (Photo by Reuters/Stringer)

A man is rushed to a hospital after he was injured during a crossfire between tribal fighters and Houthi militia in Taiz April 26, 2015. (Photo by Reuters/Stringer)

People stand by the body of a tribal fighter killed in fighting against the Houthi militia in Taiz April 26, 2015. (Photo by Reuters/Stringer)

A man is rushed to a hospital after he was injured during a crossfire between tribal fighters and Houthi militia in Taiz April 26, 2015. (Photo by Reuters/Stringer)

A Somali family waits in an ambulance with a relative injured from the ongoing violence in Yemen, as they arrive at the port of Bosasso in Somalia's Puntland region, April 26, 2015. (Photo by Abdiqani Hassan/Reuters)

A man wounded from the ongoing violence in Yemen is helped into an ambulance on arrival at the port of Bosasso in Somalia's Puntland region, April 26, 2015. (Photo by Abdiqani Hassan/Reuters)

Hundreds of families fleeing the ongoing violence in Yemen, seen arriving at the port of Bosasso in Somalia's Puntland region, April 26, 2015. (Photo by Abdiqani Hassan/Reuters)

Rubble of houses destroyed by an air raid is seen in Sanaa April 26, 2015. (Photo by Khaled Abdullah/Reuters)

People sit at the site of an air strike on houses in Sanaa April 26, 2015. (Photo by Khaled Abdullah/Reuters)

People salvage furniture from the rubble of a house destroyed by an air strike on houses in Sanaa April 26, 2015. (Photo by Khaled Abdullah/Reuters)

A dental clinic damaged in an air strike is seen in Sanaa April 26, 2015. (Photo by Khaled Abdullah/Reuters)

A Houthi militant walks past a house destroyed by an air strike in Sanaa April 26, 2015. (Photo by Khaled Abdullah/Reuters)

A house destroyed by an air strike is seen in Sanaa April 26, 2015. (Photo by Khaled Abdullah/Reuters)

A house destroyed by an air strike is seen in Sanaa April 26, 2015. (Photo by Khaled Abdullah/Reuters)

People salvage furniture from the rubble of a house destroyed by an air strike in Sanaa April 26, 2015. (Photo by Khaled Abdullah/Reuters)

A man looks from a window of his house, damaged by an air strike, at a nearby house in Sanaa April 26, 2015. (Photo by Khaled Abdullah/Reuters)

People stand at the site of an air strike in Sanaa April 26, 2015. (Photo by Khaled Abdullah/Reuters)

A guard walks inside a factory damaged after an air strike by a Saudi-led coalition struck a nearby missile base, in Yemen's capital Sanaa April 27, 2015. (Photo by Mohamed al-Sayaghi/Reuters)

A guard walks inside a house damaged after an air strike by a Saudi-led coalition struck a nearby missile base, in Yemen's capital Sanaa April 27, 2015. (Photo by Mohamed al-Sayaghi/Reuters)

A boy walks in a room as he helps to move furniture from a house damaged after an air strike by a Saudi-led coalition struck a nearby missile base, in Yemen's capital Sanaa April 27, 2015. (Photo by Mohamed al-Sayaghi/Reuters)

People carry a man injured in a crossfire during fighting between members of the Popular Resistance Committee and Houthi fighters in Yemen's southwestern city of Taiz April 27, 2015. (Photo by Reuters/Stringer)

A follower of the Houthi group holds up a sign at the site of a demonstration against the air strikes by the Saudi-led coalition in Sanaa April 27, 2015. (Photo by Khaled Abdullah/Reuters)

A boy looks out from a damaged car as he flees his home with his family following air raids in Sanaa April 11, 2015. (Photo by Khaled Abdullah/Reuters)

Followers of the Houthi group aim their weapons at a defaced poster of Yemen's President Abd-Rabbu Mansour Hadi during a demonstration against the air strikes by the Saudi-led coalition in Sanaa April 27, 2015. The words on the poster read, “Murderer of the children”. (Photo by Khaled Abdullah/Reuters)

Houthi militants gesture in the yard of the residence of the military commander of the Houthi militant group, Abdullah Yahya al Hakim, after it was hit by an airstrike, in Sanaa April 28, 2015. (Photo by Khaled Abdullah/Reuters)

A Houthi militant reacts at the yard of the residence of the military commander of the Houthi militant group, Abdullah Yahya al Hakim, after an air strike destroyed it, in Sanaa April 28, 2015. (Photo by Khaled Abdullah/Reuters)

Airport officials gather near a Felix Airways plane, destroyed by an airstrike, at the international airport of Yemen's capital Sanaa April 29, 2015. Jets from a Saudi-led alliance destroyed the runway of Yemen's Sanaa airport on Tuesday to prevent an Iranian plane from landing there, Saudi Arabia said, as fighting across the country killed at least 30 people. Airport officials said the strikes set a civilian aircraft operated by Yemeni Felix Airways ablaze. (Photo by Khaled Abdullah/Reuters)

Airport officials stand by a Felix Airways plane, destroyed by an air strike at the international airport of Yemen's capital Sanaa, April 29, 2015. (Photo by Khaled Abdullah/Reuters)

A Felix Airways plane is seen after it was destroyed by an air strike at the international airport of Yemen's capital Sanaa, April 29, 2015. (Photo by Khaled Abdullah/Reuters)

A Felix Airways plane is seen after it was destroyed by an airstrike at the international airport of Yemen's capital Sanaa, April 29, 2015. (Photo by Khaled Abdullah/Reuters)

Houthi militants ride on a patrol truck at the international airport of Yemen's capital Sanaa, April 29, 2015. (Photo by Khaled Abdullah/Reuters)

An elderly man supporting Shiite rebels known as Houthis holds his rifle as he attends a protest denounce the Saudi-led airstrikes, in Sanaa, Yemen, Monday, April 27, 2015. Yemen's exiled government on Monday declared three areas in the country engulfed in fighting between Shiite rebels, their allies and pro-government forces as “disaster” zones, including the southern port city of Aden, and said that the month of violence has claimed 1,000 civilian lives. (Photo by Hani Mohammed/AP Photo)

Boys hold up weapons to denounce the Saudi-led airstrikes as they chant slogans during a protest in Sanaa, Yemen, Monday, April 27, 2015. (Photo by Hani Mohammed/AP Photo)

In this Sunday, April 26, 2015 photo, a man carries a boy who was injured during a crossfire between tribal fighters and Shiite militia known as Houthis, in Taiz, Yemen. (Photo by Abdulnasser Alseddik/AP Photo)