A Saudi-led coalition air strike hit a hospital in Yemen's northern Hajja province on Monday, residents and local officials said, killing at least seven people and wounding 13.

A Reuters witness at the scene of the attack in the Abs district said medics could not immediately evacuate the wounded because war planes continued to fly over the area and first responders feared more bombings.

The facility is run by aid group Medecins Sans Frontieres, which confirmed on its Twitter account that an air strike had occurred there but said the number of deaths and injuries remained unclear.

A spokesman for the Saudi-led coalition did not immediately respond to a request for comment.

Another air attack hit what MSF described as a school in neighboring Saada province on Saturday, killing 10 children. The coalition said the bombing had targeted a training facility run by Yemen's dominant Houthi movement.

U.N. Secretary-General Ban Ki-moon condemned the air strike on Sunday and called for a investigation, which the coalition said it would conduct, according to a statement sent to Reuters.

Dozens of air strikes have hit civilians in Yemen since a coalition of Arab states led by Saudi Arabia began military operations in March 2015 to restore President Abd-Rabbu Mansour Hadi to power and roll back gains by the Iran-allied Houthis.

The Houthis and their allies in the General People's Congress (GPC) party headed by powerful ex-president Ali Abdullah Saleh set up a ruling council this month to run the parts of the country they control.

In its first decree on Monday, the council declared itself the "highest authority in the state (which) exercises all the powers vested in the president."

Hadi's internationally recognized government and the United Nations have criticized the council, set up after U.N.-backed peace talks in Kuwait collapsed.