The U.N. humanitarian chief says an estimated 519 people have been killed the past two weeks in Yemen's violence, many of them civilians and 90 of them children.

The deaths come as Saudi Arabia and its allies launched an air campaign on March 25 in support of President Abed Rabbo Mansour Hadi and his loyalists against Shiite rebels. Hadi's loyalists have been battling the rebels for weeks on the ground.

In a statement Thursday, U.N. Under-Secretary General for Humanitarian Affairs Valerie Amos, expresses concern "for the safety of civilians caught in the middle."

She says some 519 people have been killed and 1,700 wounded, many of them civilians, the past two weeks. Among the dead were 90 children. She says tens of thousands have fled their homes.