US grenade may have killed British aid worker during Afghan rescue attempt

American officials initially said the 36-year-old died after her captors detonated a bomb vest as American troops attempted to free her from militant kidnappers on Friday night.

But General David Petraeus, the US commander of the Nato-led force in Afghanistan, has now told Prime Minister David Cameron that a second viewing of video recordings suggested that Ms Norgrove might have been a victim of "friendly fire".

In a statement, the US military said that a review of surveillance footage and interviews with members of the rescue team "do not conclusively determine the cause of her death".

An investigation was yesterday launched by US Central Command and members of UK forces will be invited to contribute.

Describing Ms Norgrove's death as "a tragedy", Mr Cameron promised to do "everything I possibly can" to give her family certainty about her death.

The Prime Minister personally informed her family about the "deeply distressing development" in a phone call to her father John.

He said the initial reports of how the hostage died were "deeply regrettable" but were made in good faith.

Mr Cameron praised the "bravery" shown by American troops, and said it would have been "quite unorthodox" for him to insist on British special forces undertaking the mission in an area controlled by US forces.

"Linda's death is a tragedy for her family and those who worked alongside her in Afghanistan. She was a dedicated professional doing a job she loved in a country she loved," said the Prime Minister.

"I am clear that the best chance of saving Linda's life was to go ahead, recognising that any operation was fraught with risk for all those involved and success was by no means guaranteed."

The aid worker's former headteacher Ewan Mackinnon said the possibility of her having been killed by her rescuers would be "even more tragic and even more heartbreaking".

Originally from Sutherland in the Scottish Highlands, Ms Norgrove was working for the US firm Development Alternatives Inc when seized in September.