Afghan officials say a NATO airstrike killed at least 13 civilians in the eastern province of Khost on Tuesday.

NATO acknowledged Thursday that an airstrike in the Shamul district that killed four Taliban-linked Haqqani militants also killed civilians. A spokesman said the coalition had not realized the Haqqani militants were mingling with family members, including women and children, at the time of the strike.

The coalition said troops were engaged in a gunbattle with militants before calling in air support.

The mistaken killing of civilians by NATO-led forces is a major source of tension between the Afghan government and the Western backers of the international security force.

Meanwhile, a roadside bomb killed eight Afghan policemen in northern Jawzjan province. The local police chief told reporters the policemen were traveling through Fayz Abad district Thursday when their vehicle hit the explosive device.

On Wednesday, hundreds of Afghans gathered in eastern Ghazni province to protest the death of two shepherds allegedly killed in a NATO strike earlier in the day.

NATO says it is conducting a joint investigation into the incident with Afghanistan's interior and defense ministries.