Unconfirmed reports said the armed men were Afghan soldiers and police officers, Afghanistan's Khaama Press said, adding one U.S. soldier was killed following the clash.
The death of the American soldier was not confirmed by the NATO-led International Security Assistance Force.
A local government official, speaking on condition of anonymity, said the incident occurred after a verbal conflict between Afghan and U.S. soldiers at a military base in the city of Kapisa, Khaama Press reported.
ISAF issued a statement saying "Individuals wearing Afghan National army uniforms turned their weapons against International Security Assistance force members, killing one ISAF-contracted civilian. The incident is currently under investigation."