The "friendly fire" incident, which took place in Afghanistan's southern Helmand province Thursday evening, occurred after Afghan security forces called in US air support amid heavy fire from Taliban fighters just outside the province's capital, Lashkar Gah. 

The incident began after a police officer and two of his men decided to take down a Taliban flag from a nearby water tower on Thursday night, within walking distance from a police training center. When they arrived to remove the flag, police tripped a mine, which exploded and alerted the Taliban to their presence. 

The guerrillas began firing on them. Police at the nearby training center arrived to assist the first three officers but were unable to drive the Taliban back, he said.

The police unit then requested air support. Residents of Lashkar Gah heard a very loud explosion around 8:30 p.m. Thursday, they said. -Stars and Stripes

The US military says they were told that the area was clear of allied units.