PARIS (AFP) - At least 11 people were killed and more than 19 injured Monday in an airstrike on a hospital in northwestern Yemen, Doctors Without Borders (MSF) said in a statement.

The blast "partially destroyed" Abs hospital, immediately killing nine people, including an MSF staff member, while two more patients died while being transferred to another clinic, the Paris-based agency said in a statement.

It expressed outrage at what it described as "the fourth attack against an MSF facility in less than 12 months." MSF tweeted earlier that Abs, located in the rebel-held province of Hajja, "was targeted by air strikes today". It gave an earlier toll of six dead and 20 injured.

A Saudi-led Arab coalition has been battling Iran-backed rebels since March 2015 in support of Yemen's government, after insurgents seized Sanaa before moving into other parts of the country.

"Once again, a fully functional hospital full of patients and MSF national and international staff members, was bombed in a war that has shown no respect for medical facilities or patients," Teresa Sancristoval, for MSF's Emergency Unit in Yemen, said in the statement.

"Even with the recent United Nations resolution calling for an end to attacks on medical facilities and with the high level declarations of commitment to international humanitarian law, nothing seems to be done to make parties involved in the conflict in Yemen respect medical staff and patients," she said.

"Without action, these public gestures are meaningless for today's victims. Either intentional or a result of a negligence, this is unacceptable".

Earlier this month, the coalition acknowledged "shortcomings" in two out of eight cases it had investigated of UN-condemned air strikes on civilian targets in Yemen.

On Monday, it promised to probe another attack that MSF said killed 10 children over the weekend at a school in the rebel-held northern province of Saada.