U.S. and Afghan troops were fired upon while conducting an operation in eastern Afghanistan on Saturday, says U.S. military.

U.S. military spokesman Sonny Leggett reported that U.S. and Afghan personnel were conducting an operation in Nangarhar province when they were 'engaged by direct fire.'

"We are assessing the situation and will provide further updates as they become available," Leggett added.

Mohammad Ajmal Omar, a member of Nangahar's provincial council, described the shootout as a possible insider attack. Omar, who was briefed on the incident, said there appeared to be casualties among U.S. and Afghan personnel.

Insider attacks, often known as "green-on-blue" attacks, have been a regular feature of the conflict in Afghanistan, although their frequency has diminished in recent years.

There were no immediate details from U.S. officials on possible casualties or the cause of the firefight.

Taliban sources were not immediately available to comment.

The attack comes as formal peace talks between U.S. and Taliban negotiators remain hampered by the ongoing bloodshed. U.S. negotiators have demanded a reduction in violence before a deal can be signed.

Between 12,000 to 13,000 U.S. troops are serving in Afghanistan fighting terrorist groups while assisting local forces in the country.

Both the Taliban and affiliates of the terrorist group ISIL operate in eastern Afghanistan.