Mr Musharraf spoke of "sadness and anger" at Ms Bhutto's death
President Musharraf
In a televised address, he said Prime Minister Gordon Brown had agreed to send a team of detectives from London to help establish what happened.
He said "terrorists" were behind the murder, and described Ms Bhutto's death as a "great tragedy" for the nation.
Elections set for next week in Pakistan have been postponed until 18 February.
Mr Musharraf said too much damage had been done to polling stations and voter papers during the unrest in the wake of Ms Bhutto's assassination last Thursday.
He said "miscreants and political elements" had taken advantage of the situation - "looting, burning and killing".
"Election commission offices, their centres, polling stations and their equipment were all damaged and destroyed. Hence the election commission was facing a big difficulty to hold these elections [on 8 January]," he said.
Mr Musharraf said he was setting up a commission to identify who was responsible for the widespread violence, in which at least 47 people have died.
At the same time, the president promised free, fair, transparent and peaceful elections.
He called for reconciliation rather than confrontation in the run-up to the polls, and said troops and paramilitary soldiers would ensure law and order during this time.
Forensic evidence
The 30-minute speech was Mr Musharraf's first major public address since Ms Bhutto's death.
Mr Musharraf referred to "the pain and anger" of Ms Bhutto's Pakistan People's Party (PPP), especially in her home province of Sindh.
This is a very significant investigation - all the confusion that has been created in the nation must be resolved
President Musharraf
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He paid tribute to his political opponent, saying: "I also feel the same sadness and anger - I respect the sentiments of the nation."
He repeated official allegations that al-Qaeda was behind Ms Bhutto's killing, and urged the media to "expose" pro-Taleban militant leaders who, he said, were orchestrating suicide attacks in Pakistan.
He said new evidence was coming to light but that expert advice was needed, and he thanked the British prime minister for accepting his request for assistance.
"This is a very significant investigation. All the confusion that has been created in the nation must be resolved," Mr Musharraf said.
The UK's Metropolitan Police Service has confirmed that it is to send a small team from its counter-terrorism branch to provide support in the Bhutto murder inquiry.
Mr Musharraf says soldiers will keep law and order during elections
But the BBC's security correspondent Frank Gardner says that privately, British detectives are wondering how much they will be able to achieve in Pakistan as by now, nearly all forensic evidence has been lost from the crime scene and there is little usable footage of the attack.
Our correspondent says there is also the sensitive question of the exhumation of Ms Bhutto's body - something her family has so far opposed.
Unless her body is exhumed and examined by neutral experts it will be impossible to establish what actually killed her, he says.
'Bhutto's legacy'
Speaking shortly after the president's address, Ms Bhutto's widower, Asif Ali Zardari, said Britain's involvement in the investigation was too late, and should have been requested after the earlier attempt on her life in October.
Electoral posters and banners still hang from buildings in Karachi
Mr Zardari confirmed the PPP would take part in the re-scheduled elections, saying: "It is the legacy of our leader Zulfiqar Ali Bhutto to participate in elections, no matter what the circumstances."
The BBC's Chris Morris in Islamabad says the PPP wanted elections as soon as possible, in order to take advantage of what could be a big sympathy vote.
The ruling PML-Q party had said the 8 January vote should be delayed for several weeks, on the grounds that the vote would "lose credibility" if held under current conditions.
The election is seen as a crucial move towards democratic rule under President Musharraf, an important ally in the US-led "war on terror" who stood down as army chief in November.
Officials in Pakistan say parliamentary elections will be delayed until next month. VOA correspondent Nancy-Amelia Collins in Islamabad reports the Pakistan Election Commission says the delay is due to the destruction of election offices and materials in violence that broke out last week after Benazir Bhutto's assassination.

Chief election commissioner Qazi Mohammed Farooq says the elections originally scheduled for January 8 are being postponed and will be held next month.

"The polling will now be held on 18th February, 2008 instead of 8th January 2008," he said.

Election officials say they have to delay the vote because violence triggered by the assassination last week of opposition leader Benazir Bhutto destroyed a number of election commission offices and voter rolls in Sindh Province.

The opposition says the government of President Pervez Musharraf wants the election delayed to boost the votes for his supporters. The opposition has vowed to mobilize street demonstrations to protest the delay.

Political analyst Talat Masood says the government is worried the majority of votes would go to Ms. Bhutto's Pakistan People's Party, the PPP, if elections were held as originally scheduled.

"Probably they do not want to allow the PPP to catch the sympathy vote, and at the same time I think, you know, there is also an extreme resentment against the government at the moment. And president Musharraf would be in a very difficult position after the elections, because what he was wanting was a very favorable election result, so that may not be possible if the elections are held now," said Masood.

Ms. Bhutto was assassinated last Thursday while campaigning. Her supporters blame the government for failing to take adequate security measures for her safety, and Ms. Bhutto, before her death, had accused elements within the government of plotting to kill her, a charge the government denies.

A top aide to Ms. Bhutto, Senator Latif Khosa, says that on the day of her assassination, Ms. Bhutto planned to give two visiting U.S. lawmakers a thick dossier outlining numerous instances of government pre-poll rigging involving voter registration as well as intimidation of PPP supporters.

"Everything was recorded in that, with all proofs that we have had, and with the 
independent reports of the foreign monitors who were also operating. Their reports also supported our allegations as to being substantial and as being true. So they were all recorded, but unfortunately she could not present the report because she was assassinated before she could do that," said Khosa.

The government denies the allegations of vote rigging. 

The government also now says it is "open" to foreign help in investigating the assassination of Ms. Bhutto. The government of Pakistan announce that investigators from the UK will assist into the investigation into the death.

The United States government announced that it was pleased that a date had now been set for the elections.