The strike reportedly occurred during a firefight between Afghan special forces working with US advisors and Taliban insurgents late Tuesday in restive Helmand province.

NATO said air support was requested by security forces on the ground as the militants deployed heavy weapons and retreated into a nearby compound.

"After the strike, there were secondary explosions, we assess from explosives inside the compound," NATO said in a statement.

"The ground force was unaware of any civilians in or around the compound; they only knew that the Taliban was using the building as a fighting position," the statement continued.

"The Taliban continue to use civilians, especially children, as a protective measure," it added.

Afghan officials have offered varying unconfirmed numbers over how many civilians might have been killed or wounded by the strike, with one official saying the toll was at least 18 dead.

"Last night, following ground fighting in Garmsir district, foreign forces bombed some Taliban positions killing many of them. Unfortunately, we also have reports of some civilian casualties as result of the air strikes," said Omar Zhwak, the Helmand governor's spokesman.

Ataullah Afghan, the head of Helmand provincial council, said women and children were among the dead.

Ordinary Afghans have borne the brunt of the 17-year war, which is on track to be deadlier than Syria in 2018.

Civilians continue to face "extreme levels of harm", a recent UN report said, with 8,050 people killed or wounded in the January to September period this year.

Violence has intensified in the past year as US and Afghan forces step up ground and air offensives against Taliban and IS insurgents.

The Taliban has also increased attacks on Afghan forces even as the United States ratchets up efforts to engage the militants in peace talks.

Washington is trying to find a way out of the conflict more than 17 years since it began.

US envoy Zalmay Khalilzad is spearheading efforts to strike a peace deal with the Taliban before Afghanistan's presidential election, scheduled for April next year though officials have said it could be postponed until July.

A Taliban delegation met with Khalilzad in Doha in October and November to discuss ending the Afghan conflict. Khalilzad has said he is "cautiously optimistic" for an end to the conflict.

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