"Eight coalition personnel were killed and 14 others were wounded early Sunday when a coalition CH-47 helicopter had a sudden, unexplained loss of power and control and crashed in eastern Afghanistan," a coalition statement said.

"The helicopter was transporting a total of 22 people, including aircrew, at the time of the crash," it said.

The coalition said an investigation would be launched to verify the cause of the crash. It had said earlier the chopper came down after reporting engine failure.

"Recent reporting indicated a Taliban build-up for operations against the coalition forces in the region," the statement said.

Zabul is a rugged and mountainous area that sees regular clashes between security forces and fighters from the Islamist Taliban movement.

The chopper was on a transport mission and not a combat mission at the time of the crash, coalition spokesman Lieutenant Colonel David Accetta told AFP.

"The loss of these servicemembers is felt by all of us here in Afghanistan, and we offer our deepest sympathy to the families of those who were killed," he said in the statement.

The coalition would not release the exact location and details of the incident until the recovery operation was completed.

The coalition is made up of 11,000 mostly US troops who are in Afghanistan to help the government round up Taliban insurgents and their allies, including al-Qaeda militants, and to train the fledgling Afghan security forces.

There are altogether about 27,000 US soldiers in Afghanistan, some working with a separate Nato-led International Security Assistance Force.

There have been several deadly helicopter crashes, most of them accidents, involving foreign forces and other groups that deployed here after the fall of the Taliban regime in late 2001.

The last such crash was in early December, when a civilian helicopter went down between the southern city of Kandahar and Uruzgan province. All eight people on board were killed.

The Taliban claimed to have shot down the chopper, but the hardline movement regularly makes false claims. The cause of the crash was not made public.

In June 2005 a US Chinook helicopter crashed in the eastern province of Kunar, killing all 16 servicemen on board.

The US military said it was shot down by a "lucky strike" from a rocket-propelled grenade. This is the only acknowledged shooting down of a coalition aircraft in Afghanistan.

There are hundreds of foreign aircraft in Afghanistan and several air missions are carried out every day.

On Friday, 45 close-air-support missions were conducted in support of the Nato-led International Security Assistance Force (Isaf) and Afghan troops, reconstruction activities and patrols, according to the US Air Force website.

In Iraq on the same day, 56 air missions were carried out.

Isaf, which includes about 35,000 soldiers from 37 nations, works alongside the US-led coalition and Afghan security forces.