Six US servicemen were on board the UH60 Blackhawk helicopter when it crashed yesterday in the troubled Anbar province. Four soldiers were found injured and are in a stable condition.

A search and rescue mission has been launched to find the two missing servicemen after the helicopter wreckage was located by US forces.

James Hider, a correspondent for The Times in Iraq, said: "It's the US military's worst-case scenario that the guerrillas will actually get their hands on these soldiers, torture them and murder them, or hold on to them for some kind of ransom."

In June, two American soldiers were kidnapped by militants, then tortured and killed. The mutilated bodies of Private Kristian Menchaca, 23, and Private Thomas Tucker, 25, were discovered at the roadside five days later. Video footage showing a militant holding up the decapitated head of one of the two soldiers, while another armed militant stamped on the head of the other body, was also posted on an Iraqi extremist website.

Major Riccoh Player, a spokesman for the US Marines, said: “We are using all the resources available to find our missing comrades.”

The helicopter crash is not believed to have been caused by enemy fire and is the third to have happened since May. The others were both shot down by militants.

US forces rely heavily on helicopters to transport troops and supplies and to survey territory, as was the case in this flight. Many of the roads around Iraq are not regarded as safe for ground convoys because of the risk of roadside bombs and ambushes.

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