The defence ministry said it would "share the result of the investigation" into the deaths overnight in Musa Qala district, which come less than a week after a drone killed at least nine civilians in Nangarhar province east of Kabul.

Helmand's governor said 14 Taliban fighters and six foreigners "were killed in airstrikes conducted by the Afghan special forces", adding in a statement that authorities were investigating the claims of civilian casualties.

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

Majeed Akhundzada, a member of the Helmand provinical 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 civlians," he said.

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

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.