At least four people have been killed, and several others injured after a Nato aircraft crashed in southern Afghanistan, officials say.

The helicopter came down close to Qalat city, capital of Zabul province. Three US soldiers were among the dead.

A Taliban spokesman said the aircraft had been shot down, the AP news agency reported. But Nato officials say the cause of the crash is unknown.

Coalition troops are fighting the Taliban in the country's south.

Taliban spokesman Qari Yusuf Ahmedi told the Associated Press that militants had shot down the helicopter near the village of Haiz, 6km (4 miles) from Qalat, at about midnight (1800 GMT on Thursday).

But Mohammad Jan Rasool Yar, spokesman for the governor of Zabul, told AFP news agency that the helicopter "crashed last night due to technical problems."

Last month, a helicopter carrying Turkish soldiers crash landed in Wardak.

And last July, a civilian helicopter crashed in southern Afghanistan, killing at least 16 civilians and injuring five.