British aid worker Linda Norgrove was killed after a US special forces soldier failed to see that she had broken away from her captors, it has been claimed.
Ms Norgrove was already lying in a foetal position to keep safe when an American grenade was thrown during the attempt to rescue her on Friday night, The Guardian said.
The newspaper said that it had established, from sources in Kabul and London, that the soldier responsible was facing disciplinary action after failing to immediately inform his commanding officers that he had tossed the grenade.
The Guardian also claimed that the entire operation was watched on widescreen televisions at the command centre - a detail which raises further questions about why US officials initially claimed she had been killed by a bomb vest detonated by one of her captors.
The claims came as Prime Minister David Cameron was to hold Downing Street talks with General David Petraeus, the commander of international forces in Afghanistan.
A US-UK investigation is under way to establish what happened.
General Petraeus had already been due to meet Mr Cameron before the incident, but will now have the opportunity to discuss it in person.
The Prime Minister, who has already spoken with the general and US president Barack Obama about the incident by telephone, said on Tuesday that the picture was still "unclear" about how Ms Norgrove, 36, had died.
He added: "It is an impossibly difficult decision to make about whether to launch a raid and try to free a hostage. In the end we must all be clear - the responsibility for Linda's death lies with those cowardly, ruthless people who took her hostage in the first place."
Originally from Sutherland in the Scottish Highlands, Ms Norgrove was working for the US firm Development Alternatives Inc (DAI) in the east of Afghanistan when she was seized by militants in Kunar province on September 26.