The allegations stem from an overnight skirmish in Musa Qala district, less than a week after a drone killed at least nine civilians in Nangarhar province east of Kabul.

Residents and local officials in Helmand said an evening wedding celebration was underway when security forces launched a ground and aerial operation against suspected militants.

Majeed Akhundzada, a member of the Helmand provincial council, told AFP that both Afghan and foreign forces had been involved in the fighting.

"Some 40 people were killed and 18 others were wounded and were brought to the hospital, all the victims were civilians," he said.

Sher Mohammad Akhundza, a provincial senator, also put the toll at 40 dead.

Defence ministry spokesman Fawad Aman later told AFP that special forces had been targeting a compound hosting Taliban and Al Qaeda militants, saying fighting lasted an hour before an insurgent detonated a suicide vest.

Aman said at least 22 "terrorists" were killed and 14 others injured in the incident, adding that officials were investigating claims that civilians had also been killed.

But he denied that airstrikes had been used during the operation.

A statement from Helmand's governor gave a different account, saying the militants were killed in "airstrikes" and ground operations.

While the Afghan military does have a fledgling air force, most strikes are led or supported by the United States, the only member of the international coalition in Afghanistan that provides aerial support in the conflict.

There was no immediate comment from NATO's Resolute Support mission in Afghanistan.

The UN documented a sharp rise in civilian deaths from airstrikes last year, as Afghan and US forces intensified the aerial bombardment of Taliban and Islamic State group militants.