Airstrikes killed three staff workers of medical aid group Doctors Without Borders early Saturday in the Afghan city of Kunduz, the charity said. U.S. forces said they conducted airstrikes in the area.

More than 30 people remained unaccounted for after aerial bombing hit the trauma center several times, the charity said in a statement.

U.S. forces carried out a nearby strike early Saturday “against individuals threatening the force,” Army spokesman Col. Brian Tribus said.

The strike “may have resulted in collateral damage to a nearby medical facility,” he said in a statement. The military is investigating.

“We do not yet have the final casualty figures, but our medical teams are providing first aid and treating the injured patients and MSF personnel,” said Bart Janssens, operations director for the organization also known as Medecins Sans Frontieres.

When the aerial attack occurred, 105 patients and their caretakers were in the hospital. More than 80 MSF international and national staff were present.

Taliban take Kunduz

Earlier in the week, MSF hospital was caught in the crossfire between the Taliban and Afghan security forces who were supported by U.S. troops. The battle encroached on the hospital’s gate.

Bullets broke windows and punctured the roof of the intensive care unit.

The Taliban captured Kunduz city earlier this week in the group’s biggest victory in 15 years. It was a major setback for Afghan forces.

Afghanistan said it reclaimed most of the city Thursday in a big operation backed by U.S. airstrikes.

But hours later, there were signs that the Taliban were back in Kunduz, a resident told CNN. Gunshots erupted near the airport.

Kunduz is a strategic hub on the main highway between Kabul and Tajikistan.

On Thursday, Taliban fighters also took the Warduj district of Badakhshan, east of Kunduz province.