UNITED NATIONS, July 1 The United Nations inquiry into the assassination of former prime minister Benazir Bhutto formally began on Wednesday, a UN spokesman said.

He said the three members of the commission would arrive next week to start their work. They will spend a week or so at UN Headquarters in New York holding consultations and studying relevant documents ahead of their departure for Pakistan.

The commission is led by Chile's UN Ambassador Heraldo Munoz, who also heads the UN Peace-Building Commission.

The other members are former Indonesian attorney general Marzuki Darusman, who is now a member of the National Commission of Human Rights, and Ireland's former deputy police commissioner Peter Fitzgerald, who has served the UN in a number of capacities, including heading the initial mission of inquiry into the assassination of former Lebanese prime minister Rafik Hariri in 2005.

Under terms agreed to by the UN and the Pakistani government, the commission's mandate will be “to inquire into the facts and circumstances” of her death, according to an official statement issued last week.

“The duty of determining criminal responsibility of the perpetrators of the assassination remains with the Pakistani authorities,” it said.

The commission, which is expected to leave for Islamabad in the middle of July, will submit its report to Secretary-General Ban Ki-moon within six months of the start of its work. Mr Ban will share the report with the government and submit it to the Security Council for information.

Pakistan government has contributed $1.8 million towards formation of the commission. Other member states are also likely to contribute funds for the commission's work, a UN official here said.

Our Special Correspondent in London adds Interior Minister Rehman Malik told the BBC on Wednesday his government thought the UN investigation was necessary to find out who was behind the attack.

“We want to know who was behind this, who had conspired it, who has financed it. And we think this was a big international conspiracy,” the minister said.

“Obviously, there might be some actors within Pakistan or within the region, but we want really to expose the whole conspiracy, because we think that this was a kind of a beginning of an attempt to Balkanise Pakistan.”

Quoting its World Affairs correspondent Mike Wooldridge in Islamabad, the BBC said that these were challenging times in Pakistan to carry out such an investigation.

“That is not least because the Pakistan Taliban leader Baitullah Mehsud, accused by the last government here of being behind the assassination, is the target of a two-month military offensive and his militant network has hit back with retaliatory suicide attacks.

“The Taliban commander has denied having anything to do with Ms Bhutto's killing.

Benazir's assassination left questions unresolved for many people here, but especially her own party, which is now in government.

“After she had narrowly escaped a double suicide bombing on the day of her return to Pakistan from self-imposed exile in October 2007, she accused what she called 'enemies' and 'rogue elements' in the government led by President Pervez Musharraf and in the intelligence agencies of plotting to kill her.

“The UN inquiry cannot itself launch criminal proceedings, but can apparently apportion blame if it chooses to do so. Officials say the inquiry will work 'fairly discreetly'.

“Former Pakistani President Pervez Musharraf had blamed an Al Qaeda-linked militant for the attack and refused to seek a UN investigation.

“He invited police from London's Scotland Yard to assist in the inquiry into her death.

“In their report, the British detectives said they believed she died due to a severe head injury sustained as a consequence of a bomb blast.

“The Pakistani investigation into her death concluded that a lone attacker fired shots at Ms Bhutto before detonating explosives, but said that bullets were not the cause of death.

“Ms Bhutto's Pakistan People's Party (PPP) rejected both these versions, claiming adequate security had not been provided for Ms Bhutto, and called for a wider inquiry by the UN to establish the identity and motives of the assassins.”