Two U.S. service members were killed Saturday after a firefight broke out in Afghanistan, officials tell CBS News. A government official in eastern Afghanistan told CBS News the incident occurred in the Sherzad district of eastern Nangarhar province.

"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," U.S. Forces-Afghanistan (USFOR-A) spokesman Colonel Sonny Leggett said.

Six other American soldiers were wounded, according to the Afghan Ministry of Defense. They also said an Afghan National Army soldier was killed and three others were wounded.

Get Breaking News Delivered to Your Inbox

"Incidents such as this fail to have negative effects on the friendship and spirit of cooperation and between the ANDSF [Afghan National Defense and Security Forces] and U.S. Military forces," the Ministry of Defense said in a statement. "We will continue our fight against terrorism together."

The Pentagon on Sunday identified the service members who were killed as Javier Jaguar Gutierrez, 28, and Antonio Rey Rodriguez, also 28. Gutierrez was from San Antonio, Texas, and Rodriguez was from Las Cruces, New Mexico. Both were posthumously promoted to the rank of sergeant 1st class.

"We are still collecting information and the cause or motive behind the attack is unknown at this time," the statement added. "The incident is under investigation."

(L) Sergeant 1st Class Antonio Rey Rodriguez, 28, of Las Cruces, New Mexico; (R) Sergeant 1st Class Javier Jaguar Gutierrez, 28, of San Antonio, Texas. Department of Defense

It's estimated there are more than 10,000 U.S. troops in Afghanistan. In President Trump's State of the Union speech Tuesday, he said the U.S. is "working to finally end America's longest war and bring our troops back home."

Mr. Trump said "peace talks are underway," and he said it is not the "function" of the U.S. military "to serve other nations as law enforcement agencies."