The governor of eastern Logar province, Neyaz Mohammad Amiri, said that the coalition had told local authorities that the dead were Taliban insurgents, but that villagers in the remote Ab Josh area disputed that claim, saying the dead were civilians who were protecting their land from nomads.
"The reason the coalition forces fired on them is that they were heavily armed," Amiri said. "Of course it was a mistake by the coalition forces, but at the same time I blame the villagers for carrying the heavy weapons."
Security in Logar has deteriorated in recent months as the insurgents have spread their footprint across the country and taken control of some remote regions. But the war has also provided cover for local feuds, violent property disputes and organized crime.
The 13-year US-led combat mission will officially end on Dec 31. Around 13,000 US and NATO troops will remain to provide training and battlefield support.
And in neighbouring Kandahar four members of the intelligence service and a civilian were killed when their vehicle hit a roadside bomb in Dund district, the provincial police spokesman Zia Durrani said.