Last Updated Jun 10, 2014 2:45 PM EDT
KABUL, Afghanistan -- Five American troops and one of their Afghan counterparts were killed in an apparent coalition airstrike in southern Afghanistan, officials said Tuesday, in one of the worst friendly fire incidents involving United States and coalition troops since the start of the nearly 14 year war. An U.S. official confirmed to CBS News the aircraft involved in the incident was American.
A statement from the international alliance said all five soldiers died on Monday after they and their Afghan counterparts came under attack and requested air support.
Two defense officials told the Associated Press on condition of anonymity that the American troops killed were all special operations troops.
The only U.S. troops now involved in combat operations are usually Special Operations Forces that mentor their Afghan counterparts. They often come under fire and are responsible for calling in air support when needed. Because of constraints placed by outgoing Afghan President Hamid Karzai, such air strikes are usually called "in extremis," or when troops fear they are about to be killed.
A Taliban spokesman, Qari Yousef Ahmadi, said a battle took place on Monday night between foreign troops and Taliban fighters in Arghandab district in southern Zabul province.
The Afghan police chief in southern Zabul province said there was a joint operation by Afghan and U.S. troops in the province earlier Monday. After that operation was over, the troops came under an attack by the Taliban in Arghandab district and called in air support, said Gen. Ghulam Sakhi Rooghlawanay.
He told CBS News that the requested aircraft mistakenly bombed the U.S. and Afghan forces on the ground, resulting in the deaths.
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One of the worst such friendly-fire incidents came in April 2002 when four Canadian soldiers were killed by an American F-16 jet fighter which dropped a bomb on a group of troops during night firing exercise in southern Kandahar.
The Taliban claimed responsibility for the attack. The insurgents have intensified attacks on Afghan and foreign forces ahead of the country's presidential election runoff on Saturday. Officials are concerned there could be more violence around the balloting, though the first round in April passed relatively peacefully.
Along with the five NATO troops, an Afghan soldier also died in the fighting, said Rooghlawanay.
Separately, a NATO statement said a service member had died on Monday as a result of a non-battle injury in eastern Afghanistan.
The deaths bring to 36 the number of NATO soldiers killed so far this year in Afghanistan, with eight service members killed in June.
Casualties have been falling in the U.S.-led military coalition as its forces pull back to allow the Afghan army and police to fight the Taliban insurgency. All combat troops are scheduled to be withdrawn from the country by the end of this year.