KABUL—Doctors Without Borders closed its only hospital in northern Afghanistan after it was hit by U.S. airstrikes that the aid organization called a war crime, while officials launched multiple investigations into the attack.

The international medical-aid organization, also known by its French name Mé decins Sans Frontiè res, said 12 staff members and 10 patients in the Kunduz hospital were killed and much of the facility destroyed in the assault shortly after 2 a.m. Saturday.

It blamed the strikes on the U.S. military, which maintains a small presence in the country and has supported the Afghan army by ground and air in Kunduz since Taliban insurgents stormed the city last Monday.

The U.S. military said it conducted an airstrike in the vicinity of the hospital at that time to protect American special-operations forces on the ground who came under enemy fire. It acknowledged that the medical facility may have been damaged.

But it was unclear exactly where the explosives were dropped and for how long, military officials said.

"Under the clear presumption that a war crime has been committed, MSF demands that a full and transparent investigation into the event be conducted by an independent international body," Christopher Stokes, the group's general director, said Sunday. "There can be no justification for this abhorrent attack on our hospital."

Doctors Without Borders said that the hospital's main building was hit with precision for more than an hour, even after it alerted American and Afghan military officials. It said it had earlier shared its exact location with officials in Kabul and Washington.

"It was awful," said Lajos Zoltan Jecs, a nurse who survived the strike. He said he saw the intensive care unit in flames, six of its patients burning in their beds. Another patient lay dead on the operating table surrounded by rubble. "Destroying a hospital and so many lives, for nothing. I cannot find words for this."

Witnesses on Sunday said the hospital was mostly destroyed but the neighborhood was otherwise largely unscathed.

Three separate investigations were launched into the airstrikes on the hospital in Kunduz, officials said. The mission led by the North Atlantic Treaty Organization in Afghanistan said it would release the results of its preliminary investigation within days. The U.S. and Afghan governments are conducting a joint investigation, and the U.S. military is doing its own inquiry.

In the initial stages of the probes, some facts have become clear, U.S. officials said, including that American special-operations forces assisting Afghan commandos requested assistance after coming under attack by the Taliban. An AC-130 gunship was deployed to the site, either dropping munitions or firing automatic weapons in the vicinity of the hospital complex.

Investigators are trying to establish whether the hospital was mistakenly hit or whether the fire the special-operations forces were receiving was so intense that the military decided to strike Taliban fighters even if that meant hitting the hospital, said allied officials. They are also investigating whether Taliban fighters were on the premises of the hospital at the time, a U.S. military official said.

American officials left open the possibility that Taliban fighters, taking advantage of the situation, may have been responsible for some of the explosions.

Investigators hadn't yet reached the reached the site because the area wasn't secure, Defense Secretary Ash Carter said Sunday.

"The situation there is confused and complicated so it may take some time to get the facts, but we will get the facts. And we will be full and transparent about sharing them."

Afghan security officials said they believe militants were hiding inside the Doctors Without Borders compound when the attack took place, making it a potential target as Afghan forces worked to clear remaining militants from hiding places across the city.

Doctors Without Borders provides medical treatment to anyone who needs it, including insurgents. But the organization denied there were active fighters within the compound at the time of the attack. "The gates of the hospital compound were closed all night so no one who isn't staff, a patient or a caretaker was inside the hospital when the bombing happened," a spokeswoman said.

Medical staff treated those who were severely wounded in the bombing and then transferred patients to medical facilities in the cities of Pul-e Khumri and Kabul.

By Saturday night, the hospital had closed and its foreign staff had been removed from the city. Since fighting in Kunduz began last week, the hospital treated nearly 400 people and was the only advanced medical facility in Kunduz province.

The bombings repeatedly hit the main hospital building, while the rest of the sprawling compound was mostly untouched, according to Doctors Without Borders staff.

While Afghan troops have wrested back control from the Taliban of most of central Kunduz and all key government buildings, they are searching house-to-house for militants, said Kunduz police spokesman Sayed Sarwar Hussaini. Many insurgents have disguised themselves in uniforms seized from government troops, complicating the clearing operation.

On Sunday, there was sporadic fighting inside the city and Afghan troops clashed with Taliban fighters on its outskirts.

A humanitarian crisis in the city is deepening. There are shortages of medicine, food and water, residents said. The price of a loaf of bread has increased tenfold to $2.50 since Monday. On Sunday, Afghan forces began distributing food rations.

"The city is in a state of horror. Residents are too scared to leave their homes," one resident said. "The city smells of death."

Those who can are fleeing. A government employee on Saturday rented a van for $250 and drove to Kabul with his family. "There was heavy fighting in our neighborhood and there is no food to eat," he said. "What was the point in staying?"

Julian E. Barnes and Gordon Lubold contributed to this article.

Write to Margherita Stancati at margherita.stancati@wsj.com

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(END) Dow Jones Newswires

October 04, 2015 20:55 ET (00:55 GMT)