Villagers have held a protest over the deaths of three brothers allegedly killed in a raid by Nato-led forces in the eastern Afghan province of Wardak.
They said those killed overnight in Sayed Abad district were innocent.
Nato rejected the allegation, saying it had killed several suspected insurgents and detained a local Taliban commander.
Separately, the charity International Assistance Mission has blamed militants for killing 10 of its workers, including eight foreigners, last week.
A crowd of about 300 villagers yelled "Death to the United States!" and blocked a main road in Wardak during Thursday's protest.
A relative of the dead brothers, Mahmoud Khan, said US troops had entered their home in the village of Zarin Khil during the night and shot them. The soldiers then took their father into custody, he added.
"They were sleeping in one room, and suddenly the soldiers broke the glass window and they fired on them and killed them," he told the Associated Press.
However, Nato spokesman Ryan Donald said the men were "suspected insurgents", who had pointed weapons at the troops.
"The assault force engaged the threat, killing the men. After securing the compound, the assault force detained one suspected insurgent," a Nato statement said.
Correspondents say the differing accounts of the raid in question show how sensitive the Nato operation in Afghanistan has become.
In areas where the Taliban operate, it is hard to distinguish villagers from insurgents and public opinion can turn against Nato-led forces even when they are certain they have targeted the correct people, they add.
A UN report published earlier this week said that 386 civilians were killed by Nato or Afghan forces in the first six months of this year.
It said that the Taliban were responsible for 76% of civilian deaths and injuries during the same period.
Earlier, the head of International Assistance Mission said militants were "probably responsible" for shooting dead its staff in Badakhshan province last week - not thieves as previously suggested by local police.
In a statement, Dirk Frans said the medical charity was now working on the assumption that the attack had been an "opportunistic ambush by non-local fighters".
The only survivor, an Afghan man who worked as the team's driver, has now been released after questioning by the authorities.
He told investigators that he believed the lead gunmen was from Pakistan, because he had spoken words more commonly used there.