[Updated at 11:38 a.m. ET] An update on the casualties: Two American service members and two Afghan army personnel were killed in Monday's attack in eastern Afghanistan by a gunman wearing an Afghan National Security Forces uniform, ISAF and Afghan officials said.

At least 10 Americans were wounded as well, a U.S. military official told CNN.

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[Posted at 7:37 a.m. ET] Several NATO and Afghan service members were killed Monday when an assailant wearing an Afghan service uniform opened fire on the group, NATO said.

The attack happened late Monday morning in eastern Afghanistan, said Maj. Adam Wojack, a spokesman for NATO's International Security Assistance Force.

The incident appeared to be the latest so-called "green-on-blue" attack, or strike against coalition members by people dressed in police or army uniforms. Assailants conducting similar subterfuge killed dozens of coalition troops in 2012.