A Yemeni boy rolls a canister of gas he bought, after waiting for hours in Sanaa, Yemen, Tuesday, August 18, 2015. The Saudi-imposed blockade has created severe shortages of gas, petrol, and other goods, causing prices to skyrocket. (Photo by Hani Mohammed/AP Photo)

People gather at the site of a Saudi-led air strike that targeted a truck loaded with cooking oil canisters in Nqeel Yaslih near Yemen's capital Sanaa August 17, 2015. (Photo by Khaled Abdullah/Reuters)

People gather at the site of a Saudi-led air strike that targeted a truck loaded with cooking oil canisters in Nqeel Yaslih near Yemen's capital Sanaa August 17, 2015. (Photo by Khaled Abdullah/Reuters)

People gather at the site of a Saudi-led air strike that targeted a truck loaded with cooking oil canisters in Nqeel Yaslih near Yemen's capital Sanaa August 17, 2015. (Photo by Khaled Abdullah/Reuters)

A man walks at the site of a Saudi-led air strike that targeted a truck loaded with cooking oil canisters in Nqeel Yaslih near Yemen's capital Sanaa August 17, 2015. (Photo by Khaled Abdullah/Reuters)

People gather at the site of a Saudi-led air strike that targeted a truck in Nqeel Yaslih near Yemen's capital Sanaa August 17, 2015. (Photo by Khaled Abdullah/Reuters)

People gather at the site of a Saudi-led air strike that targeted a truck loaded with cooking oil canisters in Nqeel Yaslih near Yemen's capital Sanaa August 17, 2015. (Photo by Khaled Abdullah/Reuters)

People gather at the site of a Saudi-led air strike that targeted a truck loaded with cooking oil canisters in Nqeel Yaslih near Yemen's capital Sanaa August 17, 2015. (Photo by Khaled Abdullah/Reuters)

People gather at the site of a Saudi-led air strike that targeted a truck loaded with cooking oil canisters in Nqeel Yaslih near Yemen's capital Sanaa August 17, 2015. (Photo by Khaled Abdullah/Reuters)

People look at a house damaged by a Saudi-led air strike in Jibla August 17, 2015. (Photo by Reuters/Stringer)

Militants loyal to Yemen's exiled government ride atop a tank they seized from Houthi militiamen in the country's central city of Taiz August 17, 2015. (Photo by Reuters/Stringer)

Militants loyal to Yemen's exiled government ride atop a tank they seized from Houthi militiamen in the country's central city of Taiz August 17, 2015. (Photo by Reuters/Stringer)

Children walk past a tank seized by militants loyal to Yemen's exiled government from Houthi militiamen in the country's central city of Taiz August 17, 2015. (Photo by Reuters/Stringer)

Boys stand on the rubble of a sports union building destroyed by Saudi-led air strikes in Yemen's port city of Houdieda August 17, 2015. (Photo by Reuters/Stringer)

A worker walk on debris following an air strike on Yemen's Hodeida port August 18, 2015. Warplanes from a Saudi-led coalition hit the Houthi-controlled Red Sea port of Hodeida on Tuesday, destroying cranes and warehouses in the main entry point for aid supplies to Yemen's north. (Photo by Reuters/Stringer)

A graffiti riddled with bullets from fighting between militants loyal to Yemen's exiled government and Houthi militiamen is seen in Yemen's central city of Taiz August 18, 2015. Rival factions battled further south overnight in Yemen's third city, Taiz, Arab television stations reported, as local militias opposed to the Houthis attempted to consolidate recent advances on it. (Photo by Reuters/Stringer)

Militants loyal to Yemen's exiled government ride on the back of a pick-up truck during fighting with Houthi militiamen in Yemen's central city of Taiz August 18, 2015. (Photo by Reuters/Stringer)

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. (Photo by Khaled Abdullah/Reuters)

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. (Photo by Khaled Abdullah/Reuters)

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. (Photo by Khaled Abdullah/Reuters)

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. (Photo by Khaled Abdullah/Reuters)

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. (Photo by Khaled Abdullah/Reuters)

Houthi militants salvage documents from under 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. (Photo by Khaled Abdullah/Reuters)

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. (Photo by Khaled Abdullah/Reuters)

A man and his son walk past a car 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. (Photo by Khaled Abdullah/Reuters)

Houthi militants step on posters of Yemen's exiled President Abd-Rabbu Mansour Hadi 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. (Photo by Khaled Abdullah/Reuters)

Houthi militants gather 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. (Photo by Khaled Abdullah/Reuters)

A Houthi militant walks 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. (Photo by Khaled Abdullah/Reuters)

Houthi militants gather 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. (Photo by Khaled Abdullah/Reuters)

Houthi militants gather 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. (Photo by Khaled Abdullah/Reuters)

Houthi militants look at the headquarters 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. (Photo by Khaled Abdullah/Reuters)

A man walks on the rubble of his 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. (Photo by Khaled Abdullah/Reuters)

Houthi militants gather 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. (Photo by Khaled Abdullah/Reuters)

Militants loyal to Yemen's exiled government ride on the back of a pick-up truck in the country's central city of Taiz August 19, 2015. Militia forces loyal to Yemen's exiled government fought their way deep into the central city of Taiz this week, local officials said, largely pushing out Houthi militiamen from the country's third largest city. (Photo by Reuters/Stringer)