Two U.S. service members were killed and six others wounded in an apparent insider attack in eastern Nangarhar province, the U.S. forces in Afghanistan said.

Ajmal Omar, the deputy provincial council told Ariana News that the incident took place at around 7 p.m. in a military base at the center of Nangarhar’s Sherzad district.

Omar added that an Afghan army soldier opened fire on US troops and Afghan forces with a machine gun, as a result, seven US soldiers were killed.

He said the assailant was shot dead and an Afghan soldier wounded in the fire exchange.

However, Col. Sonny Leggett, a spokesman for the U.S. forces in Afghanistan said that two US service members were killed and six others wounded in the incident.

“Upon completing a key-leader engagement at the district center, current reports indicate an individual in an Afghan uniform opened fire on the combined U.S. and Afghan force with a machine gun,” said Sonny Leggett. 

He added that the incident is being investigated and the wounded service members are receiving medical treatment at a U.S. facility.

“We are still collecting information and the cause or motive behind the attack is unknown at this time. The incident is under investigation,” Leggett noted.

He said that the names of the killed soldiers are being withheld for 24 hours in accordance with the U.S. Department of Defense policy.

The two soldiers’ death brought the number of U.S. deaths in Afghanistan this year to 4.

The attack is the latest in a series of “green-on-blue” attacks in which members of the Afghan forces have killed the U.S. or coalition advisers this year.