The Saudi-led coalition bombing rebels in Yemen launched an investigation on Tuesday following international condemnation of an air strike that Doctors Without Borders said killed 11 people at a hospital it supports.
More than 19 people were also wounded in the raid that hit the hospital in Abs, in the rebel-held northern province of Hajja, the Paris-based aid agency said, adding that one of its staff was among the dead.
The hospital strike was the latest in a series of reported coalition raids hitting civilian facilities -- including at a school on Saturday that killed 10 children.
The coalition launched the bombing campaign in March last year after the Shia Houthi rebels and their allies seized control of large parts of the Arabian Peninsula nation, including the capital Sanaa.
It stepped up the air strikes earlier this month after peace talks between the rebels and President Abedrabbo Mansour Hadi's internationally backed government were suspended.
Doctors Without Borders, widely known by its French acronym MSF, said the attack was the fourth on one of its facilities in less than a year.
"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, of MSF's emergency unit in Yemen, said in a statement.
MSF said that the GPS coordinates of the hospital "were repeatedly shared with all parties to the conflict, including the Saudi-led coalition, and its location was well-known."
'String of unlawful attacks' 
Key Saudi ally Washington raised concerns about the reports, with State Department spokeswoman Elizabeth Trudeau saying: "Strikes on humanitarian facilities, including hospitals, are particularly concerning."
UN Secretary General Ban Ki-moon went further, condemning the reported strike and saying he was "deeply disturbed" by the intensification of air raids in Yemen.
"Hospitals and medical personnel are explicitly protected under international humanitarian law and any attack directed against them, or against any civilian persons or infrastructure, is a serious violation of international humanitarian law," Ban said in a statement.
Rights group Amnesty International described the bombardment as "deplorable", saying it "appears to be the latest in a string of unlawful attacks targeting hospitals, highlighting an alarming pattern of disregard for civilian life."
A Joint Incidents Assessment Team (JIAT), formed from members of the coalition dominated by Riyadh and its Gulf Arab allies, said it was aware of the reports and "has urgently launched an independent investigation".
The JIAT will "obtain more information from MSF and will publicly announce the findings" of the probe, it said.
The 14-member JIAT was set up as a standing investigation team following mounting criticism of the civilian death toll from the bombing campaign.
It earlier this month acknowledged "shortcomings" in two of eight cases it investigated of air strikes on civilian targets in Yemen.
It said the coalition had "mistakenly" hit a residential compound and an MSF-run hospital, but accused the rebels of having used the hospital as a hideout.
Rebels urge 'independent' probe 
The team is also investigating Saturday's strikes on the school in the rebels' northern stronghold of Saada. The coalition denied it had targeted the school, saying it bombed a training camp and that the rebels were using child soldiers.
A recently formed rebel council governing from Sanaa called on the United Nations to form an "independent committee to investigate" the coalition "crimes".
The so-called Supreme Political Council condemned the hospital strike in a statement on the rebels' sabanews.net website, blaming the international community whose "silence has encouraged the coalition... to commit further massacres."
The rebels formed the 10-member council late last month, in a move that put an end to the three months of UN-brokered peace talks in Kuwait.
A UN envoy has described the ruling body as a violation of commitments to the peace process.
The coalition resumed air strikes on Sanaa on August 9, less than 72 hours after the talks were suspended, with one raid reported to have hit a food factory in the city during working hours, killing 14 people.
The resumption forced the closure of Sanaa airport, but its director Khalid al-Shayef said three flights were due to arrive later Tuesday with humanitarian aid.