An air attack has killed at least 11 Afghan police officers in the volatile and opium-rich southern province of Helmand, officials said on Monday.
An interior ministry spokesman said the strike on Sunday was carried out by NATO forces but another ministry official could not confirm who was responsible.
NATO said in a statement it conducted no air strikes in Helmand on Sunday.
Afghanistan's own air force also has the capability to carry out air attacks, but both the force and the defence ministry declined to comment.
"Eleven counter-narcotics police were killed and four others were wounded in an air strike carried out by international forces in Garmsir district of Helmand province," deputy interior ministry spokesman Najib Danish told AFP.
A spokesman for the counter-narcotics police at the interior ministry confirmed the toll but could not say who carried out the attack.
US-led NATO forces ended their combat mission in Afghanistan in December, leaving local forces to battle militants alone on the ground. A 13,000-strong US-dominated residual force remains for training and counter-terrorism operations.
But there has been an escalation in air strikes by NATO forces in recent months despite the drawdown.
Foreign coalition forces carried out 106 air strikes in June, a sharp jump compared to 41 the previous month, according to NATO statistics.
That figure is still significantly lower than previous years.
US President Barack Obama has backpedalled on plans to shrink the US force in Afghanistan this year by nearly half, agreeing to keep the current level of 9,800 US troops until the end of 2015.