A US Defense Department official has anonymously confirmed to AP that five ISAF servicemen killed by friendly fire in southern Afghanistan were actually American soldiers. This could become the worst friendly-fire incident in 13 years of the Afghan War.

On Tuesday, international coalition officials confirmed that five servicemen died on Monday in what appeared to be a friendly-fire incident, without giving the details or disclosing the nationalities of the deceased.

Reportedly, the servicemen came into contact with adversaries in Arghandab district of Zabul province and came under an airstrike alongside the enemy forces.

The soldiers who died in the incident allegedly called in the airstrike that killed them.

“ISAF troops were returning to their bases after an operation when they were ambushed by the insurgents. The airstrike mistakenly hit their own forces and killed the soldiers,” shared local Police Chief Ghulam Sakhi Roghlewanai.

Qari Yousuf Ahmadi, a spokesman for the Taliban movement, claimed that a group of insurgents engaged with an ISAF unit when assault helicopters got into combat and mistakenly attacked the foreign unit.

"The casualties occurred during a security operation when their unit came into contact with enemy forces. Tragically, there is the possibility that fratricide may have been involved. The incident is under investigation. Our thoughts are with the families of those killed during this difficult time,” the ISAF announcement said.

A Pentagon statement said investigators are “looking into the likelihood that friendly fire was the cause. Our thoughts and prayers are with the families of these fallen.”

A friendly-fire incident of a similar scale took place over a decade ago, back in April 2002, when an American F-16 jet fighter dropped a bomb on a group of Canadian soldiers near a nighttime firing exercise in southern Kandahar, killing four of them.

The incident has brought the total 2014 death toll of coalition forces to 36. Of those, eight service personnel were killed in June.

If proved true, this could become probably the worst coalition friendly-fire loss of soldiers’ lives in over nearly 13 years of military campaign against the Taliban and Al-Qaeda forces in Afghanistan, just month ahead of the majority of foreign troops withdrawing from the country.