Two unidentified men dressed in Afghan military uniforms shot and killed two NATO soldiers at an Afghan military base, alliance officials report.

The incident took place early Wednesday in Helmand province and was followed by soldiers returning fire and killing the attackers, a coalition spokesperson said, according to BBC News.

Specific details about the attack are still unclear, reported The New York Times. A statement released by the American-led coalition indicates that the service members died when two men wearing Afghan uniforms opened fire on their vehicle.

However, Afghan officials in Helmand said that the two NATO soldiers had been part of a group of Americans who arrived at Camp Bastion earlier in the week. The soldiers were fired on by Afghan troops who suspected them of being Taliban fighters posing in army uniforms, a tactic the Taliban has been using in recent months, according to Yahoo! News.

"The guards on duty asked them for identification, but the American special forces seem to have ignored their warning," said Bashir Ahmad Shakir, the head of the provincial council's security committee. "The aftermath was an exchange of fire."

A representative for the international coalition in Afghanistan declined to comment on the details of the incident.

The attack is the second instance of a U.S. soldier being killed by a gunman in Afghan military uniform this year. A U.S. soldier was killed by an Afghan soldier in April after Afghan provincial leaders met a U.S. Embassy official at the compound of the Nangarhar provincial governor in the city of Jalalabad.

No party has claimed responsibility for the attack.