A Chinook helicopter from the Nato-led force in Afghanistan crashed yesterday, killing seven people on board, five of them Americans.

The Taleban claimed that it had shot down the aircraft in Helmand, the southern Afghanistan province patrolled by British and other Nato forces.

A Nato statement said: “The entire crew of five died in the incident. There were also two military passengers who died.” A US official said that five American troops had died on board the helicopter, which he said had probably been brought down by a rocket-propelled grenade. The two passengers were not Americans.

Yousuf Ahmadi, a spokesman for the Taleban, said that “our Taleban brothers” had shot down the Chinook in Helmand’s Kajaki district. “The helicopter burst into flames in the sky and then crashed. It seems that no one on board could have survived. The foreign troops have cordoned the area so we cannot have access to the area to determine the number of casualties.”

Nato said that troops arriving at the scene had also come under fire, forcing them to call in airstrikes to “eliminate the enemy threat”.

The Taleban have previously claimed to have shot down foreign military aircraft but such accounts have mostly been denied. The international forces have, however, lost several aircraft to accidents or technical failures.

The Taleban’s apparent success in downing a Chinook will ring alarm bells throughout the Nato force in Afghanistan. The British force in Helmand relies on Chinooks for transporting troops and supplies and evacuating casualties.

The RAF has seven Chinooks in southern Afghanistan in constant use. Chinooks are sturdy and have a good safety record, but yesterday’s crash has underlined the hazards faced by all helicopter crews.

Rocket-propelled grenades do not have a long range but can still be deadly against helicopters flying at low altitude. More worryingly, there is evidence that the Taleban have acquired shoulder-launched surface-to-air missiles from Iran, which have a range of more than a mile.

Helicopters are key to all operations in southern Afghanistan because of the large expanse of territory and the comparatively few troops available to defend isolated towns and villages. British troops are based in the north of Helmand province, in the Sangin Valley, and also in the south around the town of Garmsir, where the Taleban have a stronghold.

Chinooks fly daily missions to these isolated areas, dropping off ammunition, food and water for the troops. All helicopters and the Hercules transport aircraft, which also play a crucial role in Afghanistan, are vulnerable to ground fire, and crews are aware that even a burst of small arms fire can bring them down if bullets pierce the fuel tanks.

Two years ago the Taleban used a rocket-propelled grenade to shoot down a US Chinook in Kunar, killing all 16 soldiers on board.

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