Pakistani President Pervez Musharraf said on Tuesday his government was committed to finding the truth behind the assassination of opposition leader Benazir Bhutto and he vowed to punish her killers.

Bhutto, twice the nation's prime minister, was killed in a gun-and-bomb attack on December 27 shortly after she stood up through the sunroof of her armoured vehicle to wave to supporters as she left an election rally in Rawalpindi.

The government has blamed al Qaeda for killing Bhutto, a staunch supporter of the U.S.-led campaign against Islamist militancy, but many Pakistanis suspect her other enemies, perhaps from within shadowy security agencies, were involved.

A controversy has also blown up over how exactly she was killed.

Musharraf, responding to calls to seek outside help with the investigation, last week asked Britain to assist and a team of British police arrived in Islamabad on Friday.

The president met the Scotland Yard team on Tuesday and said the government was committed to "unearthing the evidence, finding out the truth and bringing those responsible for this heinous crime to justice".

"He assured the investigation team of fullest cooperation by all investigation agencies," the government quoted him as saying.

The British police said they were thoroughly sifting the evidence to ascertain the facts.

Bhutto's murder fuelled anger against Musharraf and compounded worries about security in a nuclear-armed country seen as vital to international efforts to combat al Qaeda and bring peace to neighbouring Afghanistan.

CALL FOR U.N. INVESTIGATION

A wave of violence that followed her killing led to a six-week postponement of parliamentary elections, originally set for Tuesday, to complete Pakistan's transition to civilian rule.

The elections, now due on February 18, are to elect members of the lower house of parliament, from where a new prime minister and government will be drawn to govern in cooperation with Musharraf, and of assemblies in Pakistan's four provinces.

Bhutto's Pakistan People's Party has dismissed the official account of her killing and called for a U.N. investigation.

It has also said it has no faith in the investigation.

"The Scotland Yard team had only been asked to probe the cause of death and not the perpetrators, financiers, executioners or organisers of the conspiracy," the party said.

Bhutto wrote a letter to Musharraf before she returned from eight years of self-exile in October, naming four people, including one of his political allies and the head of a security agency, that she said should be investigated if anything happened to her.

Asked last week if those people would be questioned, Musharraf said investigators would not be allowed to conduct a "wild goose chase."

Interior Ministry spokesman Javed Iqbal Cheema said the British team was independent and not being restricted.

"They're moving from the criminal scene to the criminals ... in a very systematic manner," Cheema told reporters.

The Interior Ministry said Bhutto was killed when the force of the blast smashed her head into a lever on her car's sunroof, fracturing her skull. Her party said she was shot.

Video footage showed a clean-shaven young man in sunglasses firing a pistol at Bhutto as she stood through the sunroof.

Another man photographed in the crowd with a white shawl over his head shortly before the attack was believe to be the suicide bomber, a television station said.

On Sunday, CBS News quoted Musharraf as conceding that Bhutto might have been shot.