A US military helicopter that crashed during an anti-guerrilla mission in eastern Afghanistan may have been shot down and the fate of 17 US troops aboard is not immediately known, the US military said on Wednesday.

Initial reports indicated Tuesday's crash in Kunar province, which borders Pakistan, may have been caused by hostile fire in the operation against al-Qaeda militants, the military said.

The twin-rotor CH-47 Chinook came down in remote and mountainous terrain west of Kunar's capital Asadabad, US spokeswoman Lieutenant Cindy Moore said.

Kunar Governor Asadullah Wafa said it was hit by a rocket and a spokesman for the Taliban, Abdul Latif Hakimi, claimed the guerrillas shot down the aircraft in the village of Shorak using "a new type of weapon" he did not describe.

"Initial reports indicate the crash may have been caused by hostile fire. The status of the service members is unknown at this time," the US statement said.

It said US and Afghan troops had sealed off the crash site to block any enemy movement toward or away from it and US aircraft were flying overhead.

"This is a tragic event for all of us, and our hearts and prayers go out to the families, loved ones and service members still fighting in the area," US Brig-Gen Greg Champion said in the statement.

Kunar police chief Abdul Ghafar Momand said the helicopter was thought have come down either in Shorai, around 15 km from Asadabad, or on a mountain between neighbouring Marogai and Ghaziabad districts.

"Trees caught fire on the mountain and that may have been caused by the crash, he said.

The US statement said the helicopter had been taking part in "Operation Red Wing," aimed at defeating al-Qaeda militants carrying out harassing attacks and intelligence-gathering.

The crash was the second of a US Chinook in Afghanistan in less than three months.

Another came down in a dust storm in Ghazni province southwest of the capital, Kabul, on April 6, killing 18 people, including 15 US troops, the deadliest military air accident since Washington first deployed troops to the country in 2001."

At least 14 other US troops have been killed in increased militant activity since March aimed at derailing Sept. 18 parliamentary elections, the next big step in Afghanistan's difficult path to stability.

Several US military helicopters have crashed in Afghanistan since US-led troops toppled the Taliban in 2001.

Two Chinooks were hit by rocket-propelled grenades and small-arms fire in the southwest last week and one was forced to make an emergency landing.

The Taliban's Hakimi said 35 Americans died in Tuesday's crash after the guerrillas killed 7 US "spies" on the ground, but his reports have often proven exaggerated or incorrect.

"This is a huge success for the Taliban," he said.

In early June, the US military said a helicopter had been attacked in Uruzgan province by a suspected surface-to-air missile. Such weapons, supplied by the United States, were used to great effect by guerrillas fighting Soviet occupiers in the 1980s, but the Taliban have not been known to use them.

Afghan government spokesman Jawed Ludin vowed on Tuesday the polls would be held on time despite the violence. He said fighting in the southwest last week, which the US military says killed 77 guerrillas, showed the weakness of the Taliban.

The United States leads a foreign force of about 20,000 mostly US troops pursuing militants in Afghanistan more than three and half years after toppling the Taliban for failing to hand over Osama bin Laden and other al-Qaeda leaders responsible for the Sept. 11 attacks on US cities in 2001.