An army tank fires during a firefight against militants linked to al Qaeda near the southern Yemeni city of Zinjibar May 30, 2012. (Photo by Reuters/Yemen's Defence Ministry)

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)