The Department of Defense has identified three Camp Pendleton-based Marines who were killed in Afghanistan.
The Marines died in combat in Helmand province, Afghanistan, the department said Monday.
Those killed included Capt. Matthew Manoukian, 29, of Los Altos Hills, Calf., Gunnery Sgt. Ryan Jeschke, 31, of Herdon, Va. and Staff Sgt. Sky R. Mote, 27, of El Dorado Calif.
The department stated that the combat incident is under investigation.
Military authorities told the Associated Press that a police officer shot the Marines after sharing a meal with them. The shooter has since been detained, AP reports.
The new U.S. ambassador to Afghanistan called a sudden rash of attacks on international forces by their Afghan partners "troubling" Monday, after an Afghan policeman opened fire on NATO forces in the fifth such assault in a week.
A spike in so-called "green-on-blue" attacks, in which Afghan security forces or attackers wearing their uniforms turn their guns on coalition troops, has raised concerns as NATO aims to turn over control for security to Afghan forces in a little more than two years.
"It's obviously very troubling, not just to us, but it's also very troubling to our Afghan partners," U.S. Ambassador James Cunningham told reporters in the capital in his first public comments after taking over the post earlier in the day.
"There's a lot of work being done to understand why this is happening," Cunningham said. He said it was not clear if all of the attackers were Taliban infiltrators, but noted that the strikes still threaten the "confidence and trust" needed for the two military forces to work together.
"Obviously this undermines or attacks that confidence and trust," Cunningham said.