Seven members of the Afghan security forces were killed in a NATO air strike in remote western Afghanistan, the defence ministry said on Saturday.

"Due to a NATO forces air strike on November 6 in Badghis province seven Afghan security personnel (both Afghan army and national police) were martyred and also some were wounded," the ministry said in a statement.

"The commando brigade informs us that foreign forces also sustained some casualties," it said, adding: "The issue is under investigation by Afghan and NATO forces and the results will be announced soon."

The statement comes as NATO's International Security Assistance Force (ISAF) said it was investigating an incident in Badghis Friday in which more than 25 international and Afghan forces were wounded.

Five of the 25 wounded were US soldiers, injured in what a Western military official, speaking anonymously, said was friendly fire.

However, ISAF spokesman Lieutenant Colonel Todd Vician, of the US Air Force, told AFP: "We have nothing to confirm friendly fire."

"No ISAF members were killed," he said, confirming that five injured ISAF soldiers were Americans.

Investigations into Friday's incident were ongoing and no further details were available, he said.

The incident is believed to have taken place during a clash between ISAF and Afghan soldiers who were searching for two paratroopers from the 82nd Airborne Division who went missing Wednesday during a routine supply mission.

Local police said a party looking for the two missing soldiers clashed with Taliban and that alliance aircraft were called in to provide support.

Police said the casualties occurred when the air strike mistakenly targeted international troops.

The Western military officer who spoke on condition of anonymity told AFP it appeared to be a "blue-on-blue incident," or friendly fire, with "a huge number of casualties."

NATO began its search operation in the barren, rugged area together with Afghan forces after the two paratroopers disappeared.

Afghan police said the two had drowned while trying to retrieve cartons of food that had been dropped into a river.