Troops are combing a mountainous, wooded area of militant-infested Kunar province in eastern Afghanistan to find the soldiers, US military spokesman Lieutenant Colonel Jerry O'Hara told AFP.

Sixteen personnel, including eight US Navy SEALs, were killed when their MH-47 Chinook crashed after being hit by what is believed to be a rocket propelled grenade on Tuesday. The ousted Taliban have claimed responsibility.

"The helicopter went in to lift them (the reconnaissance team) out of that area," O'Hara said.

"We have not located them as of yet, but we are doing active patrolling to find our missing US service members," he added, without saying how many personnel were missing.

The US military also said a number of Afghan guides for the US forces were also missing following the Chinook crash.

The fundamentalist Taliban said earlier this week it had captured and executed seven Afghans working as "spies" for the Americans, and that one of the men had called in the helicopter to help.

"I read those reports, since we don't know where our guides are right now, we have no proof of anything other than they are missing," O'Hara said.

The US said a major mission code named "Red Wing" was ongoing to try and find the reconnaissance team and recover all of the dead soldiers from the crash.

"Afghan national army and coalition forces remain actively engaged in Operation Red Wing," US military spokeswoman Marina Evans told AFP.

The US helicopter was the first to be shot down by hostile fire in Afghanistan and the death toll is already the biggest for US forces from a single attack since the Taliban fell in late 2001.

Lieutenant General James Conway, director of operations for the Joint Chiefs of Staff, told a Defense Department briefing in Washington late Thursday that the helicopter was downed by a "lucky shot".

The helicopter that crashed was a sophisticated special forces variant of the common CH-47 troop transport aircraft.

It is equipped with night vision equipment, a fast-rope rappelling system for deploying troops quickly and three machine guns, and is capable of refuelling in mid-flight.

Recent months have seen an escalating insurgency by the Taliban ahead of Afghanistan's landmark parliamentary and legislative elections in September.

More than 500 people, most of them militants, have died since the Taliban launched the offensive at the beginning of the year.

Coalition forces flying missions above Afghanistan's rugged terrain have suffered nine helicopter crashes since the end of 2001.

A Chinook carrying 18 people, three of them civilians, went down in an accident in bad weather in April, killing all on board in the worst air crash suffered by the United States in Afghanistan.

During a major operation against Taliban hideouts in southern Afghanistan last week, two Chinooks were hit by small arms fire. One had to make an emergency landing for repairs but then went on with its mission.

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