At least 11 people have been killed and 19 wounded in an air strike on a hospital in northwestern Yemen, according to the Doctors Without Borders (MSF) aid group, which helps run the facility.

Monday's attack on Abs hospital, located in Hajjah province, which is held by Houthi rebels, immediately killed nine people, including an MSF staff member, the Paris-based organisation said in a statement.

Two other patients died while being transferred to another hospital in Yemen, while five of the patients remained hospitalised, according to MSF.

MSF said the Arab coalition, which has been conducting air strikes in its battle against Yemen's Houthi rebels, was responsible for the hit, and asked "all parties ... to guarantee that such attacks do not happen again".

There was no immediate comment from the coalition.

Air strike has partially destroyed @MSF-supported Abs hospital in #Hajjah, #Yemen and all remaining patients and staff have been evacuated — أطباء بلا حدود-اليمن (@msf_yemen) August 15, 2016

Teresa Sancristobal, MSF emergency programme manager for Yemen, said this was the fourth attack against a facility run by the group in less than a year.

"Once again, today we witness the tragic consequences of the bombing of a hospital," she said.

"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."

At the time of the strike, there were "23 patients in surgery, 25 in the maternity ward, 13 newborns and 12 in pediatrics", MSF said.

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The attack on the hospital came two days after an air strike on a school in Haydan, in Yemen's northwestern Saada province, killed at least 10 children and wounded about 30, according to MSF.

The victims were aged between aged between eight and 15 years, the group said.

Yemen has been torn apart by conflict since 2014, when Houthi rebels, allied with ousted President Ali Abdullah Saleh loyalists, captured large swaths of the country, including the capital Sanaa.

The Arab coalition, assembled by Saudi Arabia, launched an air campaign against the rebels in March 2015.

Since then, more than 9,000 people have been killed and 2.8 million driven from their homes in fighting across the country.