Pakistan's intelligence services have been condemned in a devastating report by a United Nations inquiry into the assassination three years ago of the former prime minister Benazir Bhutto.

The report, published last night, failed to identify who was behind the assassination but concluded that Bhutto's death could have been avoided if proper security measures had been in place. It also claimed that the Pakistan police lied to a Scotland Yard forensic team that was called in to help.

However, aides to former President Pervez Musharraf angrily dismissed the report.

"There were two assassination attempts on President Musharraf by the same suicide squads that killed Benazir Bhutto. Are we saying that Mr Musharraf was responsible for the assassination attempts on himself?" said Rashid Qureshi, the former president's spokesman. "It's very strange. There's no logic behind this."

Fawad Chaudhry, Musharraf's lawyer, said that at the time of Bhutto's death in December 2007, Musharraf had handed over power to an interim government, which was overseeing elections, and had also given up his position of army chief.

"If there was any lapse, then it was the lapse of the interim government, not the president," said Chaudhry. "That's like, in Britain, holding the Queen responsible for someone's murder."

The intelligence services were heavily criticised for their role in the mishandled investigation. "The investigation was severely hampered by intelligence agencies and other government officials, which impeded an unfettered search for the truth," the report said.

Pakistan's Inter-Services Intelligence (ISI) has long been controversial largely because some senior staff have been linked to the Taliban and other extremists.

Bhutto, who had returned earlier that year from political exile, was killed by a teenage suicide bomber in Rawalpindi in December 2007. A group linked to al-Qaida was blamed.

The UN commission of inquiry began in July last year, headed by the Chilean ambassador to the UN, Heraldo Muñoz, supported by Marzuki Darusman, a former attorney-general of Indonesia, and Peter Fitzgerald, a veteran of the Irish police.

The 70-page report, which described the police's behaviour as "deeply flawed", concluded that Bhutto could have been protected if adequate measures had been taken.

"The responsibility for Ms Bhutto's security on the day of her assassination rested with the federal government, the government of Punjab and the Rawalpindi district police," it said.

"None of these entities took the necessary measures to respond to the extraordinary, fresh and urgent security risks that they knew she faced."

The damning part of the report rests in the UN team's claim of a cover-up. It said it was "mystified by the efforts of certain high-ranking Pakistani government authorities to obstruct access to military and intelligence sources".

A forensic team from Scotland Yard was involved in the investigation but the commission said its remit was narrow and it had to take much on good faith from the Pakistan police. The commission claimed the police had lied to Scotland Yard.

"That good faith was, in many respects, abused by officers of the Rawalpindi district police, particularly with respect to security arrangements. The commission's inquiry shows the accounts of the Rawalpindi police provided to Scotland Yard to be largely untrue."

The commission was baffled that the Rawalpindi police hosed down the crime scene within an hour of the murder, destroying almost all potential evidence.

The ISI is one of the most powerful organisations in Pakistan, with a pervasive reach. The commission found that the ISI conducted a parallel inquiry into the killing, gathering evidence and detaining suspects.

The commission said it believed the failure of the police to investigate Bhutto's assassination effectively was deliberate. "These officials, in part fearing intelligence agencies' involvement, were unsure of how vigorously they ought to pursue actions, which they knew, as professionals, they should have taken."

The commission does not say why the ISI hampered the investigation but offers a hint: "Given the historical and possibly continuing relationships between intelligence agencies and some radical Islamist groups that engage in extremist violence, the agencies could be compromised in their investigations of crimes possibly carried out by such groups."

The UN commission recommends reform of the police and the intelligence services. While every country needs a strong intelligence service, "the autonomy, pervasive reach and clandestine role of intelligence agencies in Pakistani life underlie many of the problems, omissions and commissions set out in this report. The actions of politicised intelligence agencies undermine democratic governance."

The ruling Pakistan Peoples party, which had been led by Bhutto, felt vindicated by the findings. The PPP had complained she was not properly protected and her assassination came from a wider conspiracy involving the military establishment.