British detectives investigating the death of ex-Pakistani Prime Minister Benazir Bhutto say she died from the effect of a bomb blast, not gunfire.
Benazir Bhutto's party disagrees with Scotland Yard's account
Detectives from Scotland Yard were asked by Pakistani President Pervez Musharraf to examine the circumstances surrounding Bhutto's death in December.
Scotland Yard's account matches that of the Pakistani authorities.
But Bhutto's party has insisted she was shot by an assassin, and has accused the government of a cover-up.
The BBC's Aamer Ahmed Khan says the exact cause of death may help shed light on who was behind the attack.
Ms Bhutto's Pakistan People's Party (PPP) has suggested that if sophisticated weaponry were used it could indicate the involvement of elements of the security establishment.
TV pictures that emerged after Bhutto's death on 27 December appeared to show a gunman aiming a weapon at the Pakistani opposition leader as she stood through the escape hatch of a vehicle during a rally in Rawalpindi.
The UK police report confirmed that shots were fired - but said they were not the cause of death.
It said after discharging his firearm the attacker had detonated explosives, blowing himself up.
"The blast caused a violent collision between her head and the escape hatch area of the vehicle, causing a severe and fatal head injury," said the report, signed by Detective Superintendent John MacBrayne.
The report said the evidence suggested there was only one attacker, not two, as had been speculated.
The BBC's Barbara Plett in Islamabad says there may be some scepticism over the report, since there has been no post-mortem on Bhutto's body, and the scene of the crime was hosed down within hours, compromising forensic evidence.
Newspapers pictured the man who apparently shot at Benazir Bhutto
However, the report said "the evidence that is available is sufficient for reliable conclusions to be drawn".
UK police reached their conclusions by studying TV footage of the assassination, and X-rays of the victim.
X-rays of Bhutto's head showed the only apparent injury was a major trauma to the right side of the head, and experts agreed this could not be a gunshot entry or exit wound, the report said.
It cited British Home Office pathologist Dr Nathaniel Cary, who said: "The only tenable cause for the rapidly fatal head injury in this case is that it occurred as the result of impact due to the effects of the bomb blast."
There were no X-rays of Bhutto's body, but Dr Cary said it is unlikely her body would have been hit by bullets through the vehicle's armour plating.
The PPP said it was not convinced by British police conclusions.
"The party is still looking at the Scotland Yard report - however, it is difficult to agree with its findings on the cause of death," party spokeswoman Sherry Rehman said.
"We do believe that she was killed by an assassin's bullet," she added.
Scotland Yard's "terms of reference were limited", she said, reiterating calls for a United Nations inquiry into the killing.
The report, released by the British High Commission in Islamabad, said determining who was behind the attack was not the job of British police, but a matter for the Pakistani authorities.
Pakistani officials said after Ms Bhutto's death that she put her own security at risk by standing up in the armoured car, with her head exposed.
Pakistani officials said on Thursday that they had made two arrests over the murder.
"We've arrested two important suspects. One of the names in Husnan Gul and the name of the second is Rufukat," announced the officer in charge of the committee investigating Bhutto's death, Chaudhry Abdul Majid.
"Apparently they were the facilitators in this case. Facilitators of the suicide bomber."
He said they were arrested following information gleaned from a 15-year old boy arrested last month in Pakistan's North West Frontier Province.
The boy said he was part of a team instructed to kill the opposition leader, and named a local militia commander, Baitullah Mehsud, as being behind the assassination, officials say.