The incident occurred Friday evening as the Afghan soldiers were heading to the district as reinforcement to International Security Assistance Forces (ISAF)-led German troops, who faced intense Taliban battle.

"ISAF forces used escalation of force procedures to stop two incoming vehicles approaching their security position," a NATO-led forces statement said. "Unfortunately after the engagement, ISAF forces discovered that the vehicles were carrying Afghan National Army soldiers in which several were regrettably killed."

NATO promised better coordination among foreign and Afghan forces as such incidents "hurt" the US-led campaign in Afghanistan.

A joint ISAF and Afghan Ministry of Defence investigation of the incident has been launched.

Kunduz governor, Mohammad Omar, called it a "tragic mistake", adding a full-scale investigation had began to probe into the incident.

Last September, dozens of Afghan civilians were among the victims of an airstrike in the same province, which was carried out on the orders of a German commander.

The airstrike targeted two fuel tankers hijacked by Taliban militants.

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