Six US soldiers have been killed in a helicopter crash in Zabul in southern Afghanistan.

Nato officials said the chopper crashed as a result of a technical problem, while the Taliban have claimed responsibility for the attack.

"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.

Nato-led ISAF military command did not provide any further details.

The Taliban claimed responsibility on Twitter, saying that its fighters shot down a helicopter while it was "flying at low altitude" over Zabul province.

The worst helicopter incident occurred in August 2011, when the Taliban shot down a transport helicopter – killing all 38 people on board.

Around 84,000 Nato-led troops are serving in Afghanistan. The number should be reduced to about 10,000 by 2015.