By Charles Haviland
BBC News, Kabul
US-led coalition forces have mistakenly shot dead 10 Afghan policemen and two civilians in central Afghanistan, a provincial official said.
US forces confirmed that four police had been wounded by insurgent fire
The Americans say they are unable to confirm such reports.
Abdullah Nashair, a spokesman for the governor of Ghazni province, said the police had gone to a site where Taleban rebels were said to have gathered.
He said US coalition forces were already on patrol there and, confusing the police for rebels, opened fire.
He said the forces also called in air strikes. Ten policemen and two civilians, one of them a woman, were found dead two hours later.
The police chief for a district in the city of Ghazni, Abdul Wakhil Kamyab, was one of those killed, Mr Nashair said.
The US-led coalition has given a different account, saying it killed several insurgents after being fired on during an operation to degrade Taleban networks.
A US spokesman said the incident was being investigated, but that they had no confirmed reports of civilian or police deaths - only of four police wounded by insurgent fire.
The incident has sparked an angry anti-American demonstration in the area.
Separately the Nato-led coalition, Isaf, said one of its soldiers was killed and two injured in an explosion during a patrol in southern Afghanistan.
Further details were not immediately available.