KABUL, Afghanistan - International medical charity Doctors Without Borders said on Sunday it has withdrawn from the northern Afghan city of Kunduz after a deadly airstrike destroyed its hospital, killing 22 people.

The humanitarian crisis in the city, which briefly fell to the Taliban last week before the government launched a counteroffensive, has grown increasingly dire, with shops shuttered because of ongoing fighting and roads made impassable by mines planted by insurgents.

"All critical patients have been referred to other health facilities and no MSF staff are working in our hospital," said Kate Stegeman, the communications manager for Doctors Without Borders, using the French acronym for the organization.

Get Breaking News Delivered to Your Inbox

"Some of our medical staff have gone to work in two hospitals where some of the wounded have been taken," she added.

Investigations are continuing into the bombing of the hospital on Saturday, which killed at least 22 people, including 12 MSF staffers.

Injured Doctors Without Borders staff are seen after an explosion near their hospital in the northern Afghan city of Kunduz Oct. 3, 2015. Médecins Sans Frontières

On Sunday, the organization announced that three injured hospital patients had died, bringing the total death toll to 22. It earlier said that three of the dead were children in the intensive care unit.

The group blames a U.S. airstrike. Afghan officials said helicopter gunships returned fire from Taliban fighters who were hiding in the facility.

In a statement released Sunday, a Pentagon spokesperson said the U.S. conducted an airstrike on a group "who were directly firing upon U.S. servicemembers advising and assisting Afghan Security Forces in the city of Kunduz. The strike was conducted in the vicinity of a Doctors Without Borders medical facility."

Afghan forces backed by U.S. airstrikes have been battling the Taliban street-by-street in Kunduz since Thursday, to dislodge insurgents who seized the strategic city three days earlier in their biggest foray into a major urban area since the U.S.-led invasion of 2001. The insurgents have had the city encircled for months, and overran it in a surprise assault that embarrassed the U.S.-backed Afghan government and called into question the competence of the U.S.-funded Afghan armed forces.

Army Col. Brian Tribus, a spokesman for American forces in Afghanistan, said Saturday a U.S. airstrike on Kunduz at 2:15 a.m. "may have resulted in collateral damage to a nearby medical facility" and that the incident was under investigation. He said it was the 12th U.S. airstrike "in the Kunduz vicinity" since Tuesday.

The U.S. Embassy in Kabul said in a statement that it "mourns for the individuals and families affected by the tragic incident at the Doctors Without Borders hospital." The statement didn't mention the airstrike.

Stegeman said there were no insurgents in the facility at the time of the bombing. AP video footage of the burned out compound in the east of Kunduz city shows automatic weapons, including rifles and at least one machine gun, on windowsills.

President Ashraf Ghani has said a joint investigation is underway with U.S. Forces. President Barack Obama said that he expected a full accounting of the circumstances surrounding the bombing.

The Taliban seized Kunduz last Monday but have since withdrawn from much of the city in the face of a government counterattack. Sporadic battles continue as troops attempt to clear remaining pockets of militants.

The Taliban's brief seizure of Kunduz marked the insurgent group's biggest foray into a major urban area since the 2001 U.S.-led invasion ended their rule.

Afghan forces have been struggling to combat the Taliban since the U.S. and NATO shifted to a support and training role at the end of last year, officially ending their combat mission in the war-torn country.

Militants blocked and mined roads as soon as they entered Kunduz to prevent people from leaving and to thwart the government's assault.

The deputy head of the Afghan National Disaster Management Authority, Aslam Sayas, said he was aware of the growing needs of people trapped inside the city. "We are waiting for the security situation to improve to give us an opportunity to reach those needy people," he said.

Saad Mukhar, the Kunduz provincial public health director, estimates that more than 70 people have been killed and more than 500 wounded in the city since the fighting began.

"I'm afraid that if this situation continues, we will not be able to help our patients because right now we are facing a serious, drastic shortage of medicine," he said.

Rahmatullah Hamnawa, a reporter with Salam Watandar radio, said cooking gas prices have more than doubled. Fuel that was 85 cents per liter before the Taliban moved in is now $1.30 per liter, he said.

Grocers and pharmacists who spoke with The Associated Press by telephone from inside the city said they make furtive deliveries after assessing the security situation.

Shir Aghan, who runs a general store, said the shops were full of food items, but many shop keepers had fled to neighboring provinces before the Taliban sealed the city. "People call me and if it's safe I'll go out and sell them what they need," he said.

Local television showed live footage of police officers handing bread to children, one of whom said he had not eaten for three days.