Linda Norgrove killed by US soldier's grenade

• A visibly shaken David Cameron addressed the press

US commander General David Petraeus phoned Prime Minister David Cameron yesterday to tell him that previous Nato reports Linda Norgrove died after her kidnappers detonated a bomb vest were incorrect.

Mr Cameron was then 45 minutes late for a press conference, where he was visibly shaken as he took to the microphone to announce the new intelligence and face questions over why he asked American forces to rescue a British national.

There will now be a joint UK and US investigation into the actions of 150 Delta Force, which carried out the operation, and Gen Petraeus is expected to be in London on Thursday to answer questions over the circumstances surrounding Miss Norgrove's death. Later Mr Cameron spoke with President Barack Obama, who offered his condolences for Ms Norgrove's death, in a telephone call to No 10 Downing Street.

A Downing Street spokesman said: "They agreed that the decision to launch the rescue operation had been right, given the grave danger to Linda's life, and that US forces had shown great courage. The Prime Minister and the President agreed that it was now essential to get to the bottom of what had happened in the course of the rescue operation.

"They looked forward to close co-operation between the UK and US authorities on the investigation and agreed to stay in close touch as it moved forward."

• Analysis: Everyone stands a risk of being killed or maimed

Charles Shoebridge, security analyst and former counter-intelligence officer, said the rescue attempt was either incompetent or based on faulty intelligence.

He said: "If you were assaulting a target you would grenade every room then go in shooting. You would not do that with a hostage situation. They were either completely incompetent or they had intelligence about which room she was in and the intelligence was faulty."

He added: "Had a typical vest bomb detonated, the room would have been destroyed and the bodies mangled out of all recognition. A grenade is very different. It's difficult to understand how the mistake could have been made.

"It's a cause for concern that the British authorities were so quick to accept what they were told."

Foreign Secretary William Hague, who authorised the failed rescue bid, paid tribute to the US forces "who risked their own lives to try to rescue a British citizen" and said there should be no doubt about who was to blame for the 36-year-old's death on Friday.

Speaking in the House of Commons, he said: "All such rescue operations involve a measure of risk which has to be weighed against a constant risk to a hostage and a risk that such an opportunity to undertake a rescue operation may not recur.

"Linda's captors were assessed to be representatives of a local Salafist group allied to the local Kunar Taleban who had links higher up the Taleban chain of command to al-Qaeda.

"We had information from the outset that the objective of Linda's captors was to pass her further up the Taleban command chain and perhaps move her to yet more inaccessible terrain.

"We were in no doubt whatsoever that there was a continual and real threat to her life and no credible option for a negotiated release."

Miss Norgrove's parents, John and Lorna, who live on the Isle of Lewis, have declined to comment as they try to come to terms with their loss. Their other daughter Sofie has returned home to be at their side. Friends said the latest reports would make her death harder for the family to accept.

Mr Norgrove said yesterday: "We might issue a statement in another day or two, we're not certain, but now we are not saying anything."

Her former teacher, Margaret MacLeod, of Uig Primary School, said: "It's absolutely shocking news and this makes it a lot harder to comprehend - especially for the parents.

"What is so shocking is why did the Americans throw a grenade into somewhere they thought she was if they were trying to rescue her? The whole community will be stunned by this new development."

Gen Petraeus informed Downing Street yesterday morning that new information suggested a grenade killed her. Mr Cameron then informed Miss Norgrove's family of the "deeply distressing development".

He said the decision to mount a rescue operation was made by Mr Hague "after careful consideration" and had his full support.

Mr Cameron said: "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."

He added: "The evidence, and subsequent interviews with the personnel involved, suggests Linda could have died as a result of a grenade detonated by the taskforce during the assault.

"However, this is not certain and a full US/UK investigation will now be launched."

Mr Cameron promised to do "everything I possibly can" to give her family certainty about how she died. He had asked "a huge number of questions" ahead of the rescue attempt and had been updated twice daily on the deliberations of the Cobra emergency committee.

Mr Cameron said: "It was right on this occasion to allow American forces to go ahead and attempt the rescue. It was part of the country that they control, ground that they know.

"In the end, you do have to listen, I think, pretty closely to the advice that you are given by commanders on the ground - Gen Petraeus and others."

Yvette Cooper, the new shadow foreign secretary, said there was "concern" about the "potentially inaccurate information that was disseminated over the course of the weekend".

A Scottish Government spokesman said: "It is essential that the US and UK investigation establishes the full circumstances of Linda Norgrove's tragic death as quickly as possible, and that the questions which this new information raises are answered - including how an apparently incorrect account came to be communicated, with the corrected position only emerging now."

Tory MP Bob Stewart, a former army officer, said: "I'm slightly worried because helicopters were used - and sometimes helicopters are heard from a long way away."

Western Isles MP Angus MacNeil said: "I have spoken to the Foreign Secretary and we had a constructive conversation - which will remain private - but we both share a desire to get to the bottom of what happened.

"I support an investigation into what's happened - everybody deserves the truth over what has happened here. The whole of the isles, from the Butt to Barra, is in shock."

A former United Nations employee, Miss Norgrove was working for the firm Development Alternatives Inc (DAI) at the time of her kidnap on 26 September. Based in Jalalabad, she supervised reconstruction programmes in the eastern region of Afghanistan funded by the US government.

James Boomgard, president and CEO of DAI, said: "Throughout this ordeal, we were satisfied that both the British and American authorities were doing everything in their power to secure Linda's release.

"Nothing has since moved us from that belief and speculating on tactics at this point doesn't move us forward in our grief or bring Linda back."