An Afghan Interior Ministry official said the shooting took place in Kapisa province, just north of the capital, Kabul.
The NATO-led coalition confirmed two foreign soldiers had been shot dead, but did not specify their nationality.
Two US defense officials, speaking on condition of anonymity, said both victims were Americans.
Four American soldiers were also wounded, one of the US officials said.
It was the first such "insider" attack this year. There were ten such incidents last year, resulting in the deaths of 15 members of the ISAF international security forces, according to Reuters' totals.
The attacks led the NATO-led force to briefly suspend all joint activities, a cornerstone of its mission in Afghanistan. REUTERS