A U.S. airstrike killed at least nine “local security personnel aligned with Afghan Government forces,” a spokesman for the U.S. military confirmed late Friday.

U.S. forces apparently mistook the police for the Taliban militants the U.S. and Afghan forces were fighting.

The airstrike took place in the Gereshk district of Helmand province, where U.S. and Afghan forces have been locked in fierce fighting with the Taliban. Local media reports put the number of dead at 17. A U.S. military statement said that an investigation would be conducted “to determine the specific circumstances that led to this incident.”

Helmand’s governor, Hayatullah Hayat, said that two commanders of the national police were among those killed and that many bodies were still under rubble, making an exact toll hard to determine.