The Pentagon says a U.S. air strike in Afghanistan's southern Helmand Province mistakenly killed a number of Afghan security forces.
Helmand provincial Governor Hayatullah Hayat on July 21 confirmed the incident and said at least two commanders were among those killed but that the total casualty toll was not yet known.
The U.S. military said its forces were supporting Afghan troops carrying out an operation against the Taliban in the province's Gereshk district when the incident occurred.
"We would like to express our deepest condolences to the families affected by this unfortunate incident," the U.S. Defense Department said in a statement.
"During a U.S.-supported ANDSF (Afghan National Defense Security Force) operation, aerial fires resulted in the deaths of the friendly Afghan forces who were gathered in a compound."
Afghan forces have been waging fierce battles to retake territory in Helmand Province, which remains largely under the control of Taliban
U.S. and other coalition forces have been in Afghanistan since 2001 helping the national government in Kabul in its battle against the Taliban and other extremist forces.