Six US soldiers from the NATO mission fighting Taliban insurgents in Afghanistan have been killed in an aircraft crash, a US defence official said, the largest death toll in a single incident to hit the international force in months.

It was not suspected to be a military strike, NATO said, adding it happened in the Zabul province of southern Afghanistan where there was no fighting reported at the time.

The Taliban immediately claimed responsibility for the deaths, saying their  fighters had shot down a US helicopter in the province of Zabul.

"The cause of the crash is under investigation, however initial reporting indicates there was no enemy activity in the area at the time," a NATO statement said.

Source: Agencies