Smoke billows from a fire at a Houthi-controlled military site after it was hit by a Saudi-led air strike in Sanaa, Yemen, June 3, 2015. REUTERS/Mohamed al-Sayaghi

School books are seen on the rubble of houses destroyed by a Saudi-led air strike near Yemen's capital Sanaa, June 3, 2015. REUTERS/Khaled Abdullah

Members of a family walk back to their home after the end of explosions from a Noquam mountain which it was hit by an air strike, in Yemen's capital Sanaa, June 1, 2015. REUTERS/Mohamed al-Sayaghi

Smoke billows from a military arms depot after it was hit by a Saudi-led air strike on the Nuqom Mountain overlooking Yemen's capital Sanaa, June 1, 2015. REUTERS/Khaled Abdullah

A Houthi militant sits amidst debris from the Yemeni Football Association building, which was damaged in a Saudi-led air strike, in Sanaa, May 31, 2015. REUTERS/Mohamed al-Sayaghi

A Houthi militant stands amidst debris from a house of a Houthi leader Rafiq Rafiq, which was destroyed by a Saudi-led air strike, near Sanaa, May 30, 2015. The Houthi militant is seen holding a picture of Rafiq Rafiq's son, who the Houthis say, was killed in the air-strike. REUTERS/Mohamed al-Sayaghi

Pepole stand near a building destroyed by a recent Saudi air strike in Yemen's northwestern city of Saada, May 29, 2015. REUTERS/Stringer

People check Saudi Air Force wreckage found in Bani Harith district north of Yemen's capital Sanaa, May 24, 2015. REUTERS/Khaled Abdullah

Houthi militants guard the house of Ali Haidar, a Houthi leader, destroyed by a Saudi-led air strike in Sanaa, Yemen, May 29, 2015. A guard was reportedly injured in the strike on the house, whose occupants had already evacuated prior to the strike, according to Houthis guarding the site and local media. REUTERS/Khale

A boy walks as he collects toys from the rubble of a house destroyed by a recent air strike in Yemen's northwestern city of Saada, May 27, 2015. REUTERS/Stringer

The body of a man is seen under the rubble of a building destroyed by a Saudi-led air strike in Yemen's southwestern city of Taiz, May 27, 2015. REUTERS/Stringer

People gather at a site hit by a Saudi-led air strike in Yemen's capital Sanaa, May 27, 2015. REUTERS/Khaled Abdullah

People gather at a site hit by a Saudi-led air strike in Yemen's capital Sanaa, May 27, 2015. REUTERS/Khaled Abdullah

Fire and smoke billows from an army weapons depot after it was hit by an air strike in Yemen's capital Sanaa, May 11, 2015. REUTERS/Mohamed al-Sayaghi

An injured woman carrying a child reacts after air strikes hit the house of Yemen's former President Ali Abdullah Saleh in Sanaa, May 10, 2015. REUTERS/Mohamed al-Sayaghi

A man screams in front of the residence of Yemen's former President Ali Abdullah Saleh after airstrikes hit it in Sanaa, May 10, 2015. REUTERS/Mohamed al-Sayaghi

People flee as smoke billows after air strikes hit the house of Yemen's former President Ali Abdullah Saleh in Sanaa, May 10, 2015. REUTERS/Mohamed al-Sayaghi

Smoke rises during an air strike on an army weapons depot on a mountain overlooking Yemen's capital Sanaa, April 20, 2015. REUTERS/Khaled Abdullah

The wreckage of a Yemeni air force military transport aircraft is seen on the tarmac after the aircraft was destroyed by an air strike, at the international airport of Yemen's capital Sanaa, May 5, 2015. REUTERS/Khaled

A girl cries next to her mother after fleeing from an air strike on an army weapons depot in Yemen's capital Sanaa, May 11, 2015. REUTERS/Mohamed al-Sayaghi

People ride on a motorcycle as they pass by a police headquarters destroyed by a Saudi-led air strike in Yemen's northwestern city of Saada, May 7, 2015. REUTERS/Khaled Abdullah

Smoke billows from a Noqum mountain after it was hit by an air strike in Yemen's capital Sanaa, May 19, 2015. REUTERS/Mohamed al-Sayaghi

A view shows damage in a factory, caused by an air strike on Monday that hit a nearby army weapons depot, in Sanaa, April 21, 2015. REUTERS/Mohamed al-Sayaghi

A plainclothes presidential guard stands in front of the residence of Yemen's former President Ali Abdullah Saleh after airstrikes destroyed it in Sanaa, May 10, 2015. REUTERS/Mohamed al-Sayaghi

An air strike hits a military site controlled by the Houthi group in Yemen's capital Sanaa, May 12, 2015. REUTERS/Khaled Abdullah

People stand on the rubble of houses destroyed by an air strike in the Okash village near Sanaa, April 4, 2015. REUTERS/Mohamed al-Sayaghi

A police trooper walks on a street littered with debris by an air strike on a nearby Scud missile base in Yemen's capital Sanaa, April 20, 2015. The air strike on a Scud missile base in the Yemeni capital Sanaa caused a big explosion that blew out windows in homes, killing seven civilians and wounding dozens, medical sources told Reuters. REUTERS/Khaled Abdullah