ISLAMABAD — President Musharraf announced today that Scotland Yard will help investigate the assassination of Benazir Bhutto, and authorities pushed back elections until February 18 — a delay prompted by the rioting that followed her death.

Opposition parties condemned the six-week postponement but still plan to take part in the parliamentary elections, seen as a key step in bringing democracy to Pakistan after years of military rule.

Both developments could ease the turmoil that has gripped Pakistan since Bhutto’s slaying in a gun and suicide bomb attack last week, which plunged the nation deeper into political crisis as it struggles to contain an explosion of Islamic militant violence.

The government declared just one day after the attack on Bhutto that an Al Qaeda-linked militant orchestrated the killing and aired video footage. But the hasty accusation only served to cast doubt over the government’s account of exactly how the opposition leader died.

The government has also come under sharp criticism for its security arrangements for Bhutto, who had claimed elements in the ruling party were trying to kill her.

In a nationally televised address today, a solemn-faced Mr. Musharraf said the death of Bhutto, a two-time prime minister, was a great tragedy for Pakistan. He blamed “terrorists” for her assassination and appealed for public unity to combat them.

“This is a time for reconciliation and not for confrontation,” he said.

Reversing the government’s initial stand that it did not need foreign help to probe the killing, Mr. Musharraf said he sought assistance from Prime Minister Brown. That could quell calls for an independent, international investigation.

Scotland Yard said it was sending a small team of officers from the Metropolitan Police’s Counterterrorism Command. The British foreign secretary, David Miliband, said the team would leave Britain by the end of the week.

The White House said it supported Scotland Yard’s involvement, adding that a United Nations investigation into Bhutto’s slaying was not necessary now.

“Scotland Yard being in the lead in this investigation is appropriate and necessary and I don’t see — we don’t see a need for an investigation beyond that at this time,” a presidential spokeswoman, Dana Perino, said.

The White House would not comment on why Mr. Musharraf rejected an apparent American offer to help with the inquiry.

“What’s most important is that they proceed quickly and in a transparent and comprehensive way, so that the people of Pakistan can get the answers that they deserve, and that, as they move forward toward the elections with the date certain that was just set today, the people will be able to participate in a process freely,” Mr. Perino said.

A spokesman for the director of American national intelligence, Ross Feinstein, said his agency has yet to reach any conclusions over who was responsible for the killing.

Bhutto’s husband and now chief of her party, Asif Ali Zardari, has demanded a U.N. committee investigate her assassination, similar to the probe of the 2005 bombing death of a former Lebanese prime minister, Rafik Hariri.

Rioting that erupted after Bhutto’s death has killed nearly 60 people and caused tens of millions of dollars in damage, particularly in her home province of Sindh. Referring to the violence, Mr. Musharraf accused “many miscreants and some political elements” of taking advantage of the tragedy to loot and plunder.

But he had reconciliatory words for Bhutto’s supporters, saying their slain leader had wanted to promote democracy and end terrorism.

Mr. Musharraf, who took power in a 1999 coup and recently declared six weeks of emergency rule in an apparent bid to cling to the presidency, said he had wanted elections to go ahead as planned on January 8. But he supported the decision to delay the vote until February 18 because of the rioting.

While Bhutto’s party condemned the delay and said the government did not sincerely want to hold fair elections, Mr. Zardari said their party would run anyway — a boost to Mr. Musharraf’s hopes to engineer a democratic transition. Mr. Zardari backed off from threats to call street protests if the vote was postponed.

“We have decided to take part in the election,” he said. “People should be peaceful and express their anger through their ballots.”

The party of a former prime minister, Nawaz Sharif, quickly followed suit.

“We will not leave the field open for the king’s party under any circumstances,” a party spokesman, Ahsan Iqbal, said, referring to the ruling party, which is allied to Mr. Musharraf.

The opposition alleged authorities were postponing the vote to help the ruling party, amid expectations that Bhutto’s group could get a sympathy boost at the polls. The ruling party could also suffer a backlash because of Bhutto’s claims it had plotted to kill her, a charge it vehemently denies.

A ruling party spokesman, Tariq Azim, denied his group would benefit from the delay.

The head of the election commission, Qazi Mohammed Farooq, said the unrest after Bhutto’s dead, which led to the destruction of 10 election offices, made it impossible to hold the election on time.

However, an independent political analyst, Talat Masood, said the delay was “mostly about politics.”

“The (election) problems are only confined to a few districts. Musharraf naturally thinks if a hostile parliament comes in, he has no future.”

Pakistani troops, meanwhile, killed up to 25 suspected militants yesterday in a remote region close to the Afghan border where Al Qaeda and Taliban fighters operate. The fighting followed the abduction of four soldiers, an army spokesman, General Waheed Arshad, said.

The government has blamed a South Waziristan-based militant leader, Baitullah Mehsud, for Bhutto’s murder; he has denied involvement.

In his address, Mr. Musharraf did not explicitly blame Mr. Mehsud. But he appealed to the media and Pakistanis to “expose” him and another prominent pro-Taliban militant leader based in the Swat Valley, Mullah Fazlullah, whom he also accused of orchestrating suicide attacks.