Friendly fire is being blamed for the deaths of five foreign servicemen in southern Afghanistan.
Police and Taliban insurgents say they were killed by fire from helicopters piloted by their own allies on Monday.
The International Security Assistance Force gave no reason for the deaths in southern Zabul province, days before a run-off round in a presidential election, Reuters reports.
The force is investigating the deaths.
Local police chief Ghulam Sakhi Roghlewai said ISAF troops were returning to their bases after an operation when they were ambushed by the insurgents and the air strike mistakenly hit their own forces.
Taliban spokesperson Qari Yousuf Ahmadi said insurgents were attacking the foreign forces when the helicopters intervened and accidentally killed their own troops.
Security is being ramped up ahead of Saturday's run-off vote to replace President Hamid Karzai.
The poll pits Abdullah Abdullah, a forrmer leader of the opposition to the Islamist Taliban, against former Finance Minister Ashraf Ghani.