The police chief of Farah's Anar Dara district is in a serious condition after the raid, Rasouli said.

Investigation under way

Isaf has said that the air raids were carried out by the separate US coalition.

James Bays, Al Jazeera's correspondent in Kabul, said he had heard a report that an Amercian Apache helicopter had targeted [the] policemen.

Ikramuddin Yawar, the police commander for western Afghanistan, said a team had been despatched to the area to investigate.

"Last night at around 1:30, a clash took place between ANA, ANP [Afghan National Police] and Isaf, each mistaking the other side as Taliban," Yawar said.

The Afghan defence ministry and Nato said they had no details on the incident, but were looking into the reports.

There have been several instances in Afghanistan where Afghan and Nato security forces have mistaken each other and launched deadly attacks.

The forces have been accused of not properly co-ordinating their operations against Taliban loyalists, resulting in cases of mistaken identity.

Nato raid

Also on Sunday, Nato's Isaf contingent said it is responsible for the deaths of four Afghan civilians late on Saturday.

The incident occurred late Saturday in Paktika province, close to the border with Pakistan, Isaf said in a statement.

"An Isaf unit on a fire mission accidentally killed four civilians, with an unconfirmed further three deaths," the statement said.

Two mortar rounds fired by an Isaf unit missed their intended target by about a kilometre, Isaf said.

"Four civilians were also wounded and are now under treatment  by Isaf forces," the statement said.

Isaf said it "deeply regrets" the incident.