DOHA (Reuters) - Medecins Sans Frontieres (MSF) said it was evacuating its staff from six hospitals in northern Yemen on Thursday after a Saudi-led coalition air strike hit a health facility operated by the medical aid group killing 19 people.

"Given the intensity of the current offensive and our loss of confidence in the Saudi-led coalition to prevent fatal attacks, MSF considers the hospitals in Saada and Hajjah governorates unsafe for both patients and staff," the group said in a statement.

Countless attacks on health facilities in Yemen have endangered patients and staff and displayed a failure by warring parties to control the use of force, the group said.

MSF is one of handful of international medical aid groups operating on the ground in Yemen where a 16-month civil war between a Gulf Arab coalition and an Iran-allied militia has killed over 6,500 people and brought one of world's poorest countries close to famine.

On Tuesday a Saudi-led coalition air strike hit a hospital operated by MSF in the northern Hajja province injuring 24 and killing 19 people including one of its staff members, the group said.

Another air attack on Saturday hit what MSF described as a school in neighboring Saada province, killing 10 children.

U.N. Secretary-General Ban Ki-moon condemned the air strike and called for a investigation, which the coalition said it would conduct.

MSF said it had met with officials from the Saudi-led coalition and shared GPS coordinates of the hospital it operates in with parties involved in the conflict but aerial bombings had continued.

"The decision to evacuate the staff from a project is never taken lightly but in the absence of credible assurances that parties will respect the protected status of medical facilities there may be no other option," said the statement.

Dozens of Saudi-led air strikes and shells launched by the Houthis have hit civilians in Yemen since the Arab coalition began military operations in March 2015 to restore President Abd-Rabbu Mansour Hadi to power.

The cost from damage to infrastructure and economic losses in the civil war is more than $14 billion so far, according to a confidential report seen by Reuters.

(Reporting by Mohammed Ghobari; Writing by Tom Finn; Editing by Toby Chopra)