According to MSF, the attack resulted in the deaths of 10 patients and a staff member of the aid group
At least 11 people were killed and 19 wounded when an air strike hit a hospital operated by Medecins Sans Frontieres (MSF) in Northern Yemen on Monday, the medical aid group said.
The air strike, believed to have been conducted by the Saudi-led coalition, took place in the Abs district of Hajja province and according to MSF, resulted in the deaths of 10 patients and a staff member of the aid group.
A witness at the scene of the attack said medics could not immediately evacuate the wounded because war planes continued to fly over the area and emergency workers feared more bombings, Reuters reported.
"The location of the hospital was well known, and the hospital's GPS coordinates were repeatedly shared with all parties to the conflict, including the Saudi-led coalition," the aid group, also known as Doctors Without Borders, said in a statement.
"This is the fourth attack against an MSF facility in less than 12 months," the statement said.
"Even with the recent United Nations resolution calling for an end to attacks on medical facilities and high-level declarations of commitment to international humanitarian law, nothing seems to be done to make parties involved in the conflict in Yemen to respect medical staff and patients."
In response to an Associated Press request for comment, the Saudi-led coalition said its Joint Incidents Assessment Team "is aware of reports of an air strike on a hospital in Yemen's northern Hajjah province."
The coalition assessment team has opened an investigation into these reports as a matter of urgency and is seeking additional information, in particular from MSF, the statement said.
Another air attack hit what MSF described as a school in neighbouring Saada province on Saturday, killing 10 children. The coalition said the bombing had targeted a training facility run by Yemen's rebel Houthi group.
UN 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 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."
Over the last weeks @MSF-supported Abs hospital witnessed increase in patients, mostly victims of recent clashes & aerial campaign in area— - (@msf_yemen) August 15, 2016
Hadi's internationally recognised government and the United Nations have criticized the council, set up after UN-backed peace talks in Kuwait collapsed.
In Washington, the State Department said it was "deeply concerned by a reported air strike" and called on "all parties to cease hostilities immediately," but did not specifically point to the Saudi-led coalition.
According to the UN, more than 6,400 people, mostly civilians, have been killed in Yemen since last March.