Women displaced by the fighting in Yemen collect water at a camp fin the northern province of Amran, Yemen, 10 August 2016. (Yahya Arhab/EPA)

An airstrike by a U.S.-backed Saudi-led military coalition struck a Doctors Without Borders hospital in northwestern Yemen on Monday, the latest bombing of a civilian site since a peace deal between the nation’s warring factions collapsed last week.

Abs Hospital, located in the country’s Hajjah governorate and supported by the international medical charity, was hit at 3:45 p.m. local time, Doctors Without Borders said in a statement. The number of casualties was not yet known, though reports on social media suggested that as many as 20 people might have been killed or wounded.

“MSF is currently assessing the situation to ensure the safety of patients and staff,” the aid agency, using the acronym for its French name, Medecins Sans Frontieres, said in its statement. “We will provide more information as it becomes available.”

More than 4,600 patients have been treated at the hospital since the charity began supporting it in July 2015.

The bombing comes two days after a Saudi-led coalition airstrike hit a Koranic school in an enclave of the northern city of Saada, killing 10 children and wounding 28. All were between the ages of 6 and 15, according to Doctors Without Borders, whose staff treated the victims at their facility there.

Saudi Arabia’s military has said that Saturday’s airstrike struck a militia training camp but offered no evidence for its claims. A 14-member team set up by the coalition to investigate allegations of wrongdoing said it had opened an inquiry into reports that the school was hit and would make its findings public.

There was no immediate comment from Saudi Arabia on Monday’s airstrike, which was at least the fourth on a Doctors Without Borders-supported medical facility in Yemen since the war began in early 2015. Last year, one person was killed in an airstrike on a health center in Saada province, and a mobile clinic in the southern province of Taiz was also hit, according to the aid agency. In January, another hospital in Saada was targeted, killing six.

Several organizations working in Yemen condemned Monday’s attack and called for an independent investigation.

“This was a horrific attack killing sick and injured people and the medical staff desperately trying to help them,” said Sajjad Mohammad Sajid, Oxfam’s country director in Yemen. “The world cannot continue to turn a blind eye as the most vulnerable suffer in this terrible conflict.”

“Today’s air strike appears to be the latest in a string of unlawful attacks targeting hospitals highlighting an alarming pattern of disregard for civilian life,” Magdalena Mughrabi, Amnesty International’s deputy director of the Middle East and North Africa Program, said in a statement.

“The bombardment of this hospital is a deplorable act that has cost civilian lives, including medical staff who are dedicated to helping sick and injured people under some of the most challenging conditions,” Mughrabi said. “Deliberately targeting medical facilities is a serious violation of international humanitarian law which would amount to a war crime. The circumstances of this attack must be thoroughly and independently investigated.”

On one side of the conflict is Yemen’s President Abed Rabbo Mansour Hadi, who is backed by Saudi Arabia, the United States and their allies. On the other side is an alliance between Shiite Houthi rebels and loyalists of former president Ali Abdullah Saleh. They seized the capital, Sanaa, and drove Hadi southwards to the port city of Aden.

Sunni-led Saudi Arabia, concerned about the Houthis and their links to its main regional rival, Iran’s Shiite theocracy, entered the war to restore Hadi to power.

More than 6,500 people have died in the war, around half of them civilians. The Middle East’s poorest nation, in crisis long before the war began, is now in the throes of a humanitarian disaster.

Human rights groups have accused the Saudi-led coalition of human rights violations, which Riyadh has denied. The Houthis have also been accused of abuses, including the recruitment of child soldiers and forced disappearances of their opponents.

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