Officials said several other people were wounded in the so-called insider attack at a police station, the BBC reported.
Abdul Razaq Quraishi, the deputy provincial police chief, and NATO officials confirmed the deaths, Khaama Press reported.
The killings in Wardak province came a day after U.S. special forces withdrew from the province. The Afghan government had demanded the withdrawal after allegations of disappearances and torture by Afghan troops working with the Americans, the BBC said.
Officials told the BBC the shooter either was a local police officer or an insurgent posing as one.
The police station incident was the latest "green-on-blue" attack, those against coalition members by people wearing Afghan police or army uniforms.
On Friday, a coalition contractor was killed when people in Afghan National Army uniforms fired on ISAF members, NATO said.
Also Monday, police in the Afghan capital of Kabul said two civilian truck drivers were killed and one wounded when they were fired upon by an ISAF convoy, the BBC said. A coalition spokesman said the troops opened fire to protect themselves when the two drivers failed to comply with a warning from the convoy.