KABUL, Afghanistan  At least nine Afghan police officers and a civilian were killed early Thursday in a firefight between American forces and the officers in Ghazni Province, just south of the capital, local officials said.

The American forces were searching houses in a village on the outskirts of Ghazni town and blew open the gates of a house, according to local Afghan officials. District police officers heard the explosion and rushed to the scene, suspecting that the Taliban were in the area, but were themselves mistaken for Taliban and shot by the American soldiers, the officials said. Aircraft supporting the operation fired on one of the police cars.

The killings set off protests in the town on Thursday afternoon, and demonstrators blocked the main highway and prevented a government delegation from reaching the town from a nearby airfield, local officials said.

“Another big cruelty was made by American forces this morning,” said Khial Muhammad Hussaini, a member of Parliament from the province who was among the elders and legislators who had traveled to the town to try to calm people and persuade them to reopen the highway.