The Pentagon is investigating the deaths of five U.S. troops who were reportedly killed from friendly fire during a clash with Taliban forces in southern Afghanistan on Monday.

CNN reported that the American service members were killed when a coalition jet mistakenly bombed them after it was called in to help ward off a Taliban attack. An Afghan soldier also died in the apparent friendly fire strike in the Zabul province, Afghan official Ghulam Sakhi Roghliwanai said.

The service members called in air support, "but the airstrike mistakenly bombed their own friends too," he said.

According to NATO, the troops were conducting a security operation, ahead of Afghanistan's upcoming presidential runoff election this Saturday.

A U.S. military official told CNN that the service members' unit came in contact with enemy forces, which is when the casualties occurred. "There is the possibility that fratricide may have been involved," he said.

Pentagon Press Secretary Navy Rear Adm. John Kirby released a statement Tuesday confirming the deaths: "Five American troops were killed yesterday during a security operation in southern Afghanistan. Investigators are looking into the likelihood that friendly fire was the cause. Our thoughts and prayers are with the families of these fallen," the LA Times reported.

The coalition headquarters in Kabul also issued a statement but did not include the nationalities of the casualties. "Tragically, there is the possibility that fratricide may have been involved," the coalition statement reads.

Provincial police chief Gen. Ghulam Sakhi Rooghlawanay told The Associated Press that after a joint operation by Afghan and NATO the troops were under attack from the Taliban.

"The joint forces came under the attack of insurgents, and then foreign forces called for air support," he told AP. "Unfortunately five NATO soldiers and one Afghan army officer were killed mistakenly by NATO airstrike."

Afghanistan's Pajhwok Afghan News reported that an interpreter was killed.