KABUL (Reuters) - Five U.S. servicemen were killed in southern Afghanistan in a friendly-fire air strike during a security operation, Afghan police said on Tuesday, days before a run-off round in the country's presidential election.
The International Security Assistance Force (ISAF) said the casualties occurred on Monday when the unit came into contact with enemy forces. It did not give the nationality of the dead soldiers.
Local police chief Ghulam Sakhi Roghlewanai said of the incident in Zabul province's Arghandab district: "The five killed were American soldiers who just returned from an operation when they were hit.
"ISAF troops were returning to their bases after an operation when they were ambushed by the insurgents. The air strike mistakenly hit their own forces and killed the soldiers."
A Taliban spokesman, Qari Yousuf Ahmadi, said insurgents had been attacking the foreign forces when the helicopters intervened and accidentally killed their own troops.
The Islamist Taliban, removed from power by a U.S.-led drive into Afghanistan after the September 11, 2001 attacks, is on an offensive ahead of the planned withdrawal of most foreign troops by the end of 2014.
An ISAF statement said an investigation was under way into "the possibility that fratricide may have been involved".
Security is being ramped up in Afghanistan ahead of Saturday's run-off vote to replace President Hamid Karzai.
The poll pits Abdullah Abdullah, a former leader of the opposition to the Islamist Taliban, against former Finance Minister Ashraf Ghani.
(Reporting by Hamid Shalizi; Writing by Praveen Menon; editing by Ron Popeski)