KABUL — U.S. forces may have mistakenly bombed a hospital in northern Afghanistan on Saturday, killing at least 19 people, including three children, in an incident that will likely raise new questions about the scope of American involvement in the 14-year war.

In a statement, Doctors Without Borders said an airstrike “partially destroyed” their trauma hospital in Kunduz, where the Afghan military has been trying to drive Taliban fighters from the city.

The airstrike killed at least 12 Doctors Without Borders staff members, the group said. Three children were also reportedly killed. At least 37 other people were seriously injured, including 19 staff members and 18 patients and caretakers. Officials warned the death toll could rise as dozens of people remain unaccounted for.

“This attack is abhorrent and a grave violation of International Humanitarian Law,” Meinie Nicolai, the group’s president, said in a statement. “We demand total transparency from Coalition forces. We cannot accept that this horrific loss of life will simply be dismissed as ‘collateral damage.’”

Defense Secretary Ashton Carter issued a statement saying: “While we are still trying to determine exactly what happened, I want to extend my thoughts and prayers to everyone affected. A full investigation into the tragic incident is underway in coordination with the Afghan government.”

Over the past week, U.S. military jets have conducted numerous airstrikes in Kunduz after the Taliban overwhelmed Afghan security forces on Monday. American Special Operations troops and on-the-ground military advisers from the NATO coalition also have been assisting Afghan forces. Doctors Without Borders was one the last remaining international relief organizations in Kunduz.

In a statement, the U.S.-led coalition confirmed it carried out an airstrike about 2 a.m. Saturday in response to “individuals threatening the force.”

“The strike may have resulted in collateral damage to a nearby medical facility,” said Col. Brian Tribus, a spokesman. “This incident is under investigation.”