KABUL, Afghanistan — A large Taliban explosion targeting an elite Afghan militia force that has worked closely with the C.I.A. killed at least a dozen people on Saturday in the eastern part of the country, officials said.

Gen. Faizullah Ghairat, the police chief of Khost Province, which borders Pakistan, said that members of the Khost Protection Force, a militia trained and paid for by the United States, were returning from a mission and had stopped at a crowded bazaar when a car bomb exploded.

There were conflicting reports about the death toll. Najib Danish, a spokesman for the Interior Ministry, put the number at 18, while another senior security official said 13 people had been killed.

It was not immediately clear how many of the casualties were civilians or members of the militia, known as K.P.F.