Nine members of the Nato-led International Security Assistance Force have been killed in a helicopter crash in southern Afghanistan, officials say.

九名由北约领导的国际安全援助部队成员死于阿富汗南部的直升机坠机事故。

One Nato soldier, an Afghan soldier and a US civilian¹ were also injured, an Isaf statement said. The nationalities of the Nato personnel are not known.

It is not yet clear what caused the crash, but Isaf said there was no enemy fire where the aircraft came down.

At least 529 foreign troops have been killed so far this year in Afghanistan.

The toll² makes 2010 the deadliest year since the US-led invasion in 2001, according to figures collated³（整理，核对） by the website iCasualties.

Isaf did not give the exact location of Tuesday's incident in its statement.

"The cause of the crash is under investigation," it said. "There are no reports of enemy fire in the area."

The three injured have been taken to an Isaf medical facility for treatment. An Isaf spokesman said more information would be released later.

There are almost 150,000 foreign troops fighting the Taliban in Afghanistan, supporting about 300,000 Afghan security forces.