RAWALPINDI, Pakistan — A Pakistan opposition leader, Benazir Bhutto, was assassinated today by an attacker who shot her after a campaign rally and then blew himself up. Her death stoked new chaos across the nuclear-armed nation, an important American ally in the war on terrorism.

At least 20 others were also killed in the attack on the rally for January 8 parliamentary elections where the 54-year-old Bhutto had just spoken.

Bhutto’s supporters erupted in anger and grief after her death, attacking police and burning tires and election campaign posters in several cities. At the hospital where she died, some smashed glass and wailed, chanting slogans against President Musharraf.

RELATED: Bhutto’s Life Was an Epic of Blood and Controversy | Bush Denounces ‘Cowardly Act’ | The Scramble for Culprits Begins

The death of the charismatic former prime minister threw the campaign for the parliamentary elections into chaos and created fears of mass protests and violence across the nuclear-armed nation, an important American ally in the war on terrorism.

Mr. Musharraf convened an emergency meeting with his senior staff where they were expected to discuss whether to postpone the election, an official at the Interior Ministry said, speaking on condition of anonymity because of the sensitivity of the talks.

No one claimed responsibility for the killing. But suspicion was likely to fall on resurgent Islamic militants linked to Al Qaeda and the Taliban who hated Bhutto for her close ties to the Americans and support for the war on terrorism. A local Taliban leader reportedly threatened to greet Bhutto’s return to the country from exile in October with suicide bombings.

The attacker struck just minutes after Bhutto addressed thousands of supporters in the garrison city of Rawalpindi, 8 miles south of Islamabad. She was shot in the neck and chest by the attacker, who then blew himself up, Bhutto’s security adviser, Rehman Malik, said.

A leader from Bhutto’s party, Sardar Qamar Hayyat, said he was standing about 10 yard away from Benazir Bhutto’s vehicle at the time of the attack.

“She was inside the vehicle and was coming out from the gate after addressing the rally when some of the youths started chanting slogans in her favor. Then I saw a smiling Bhutto emerging from the vehicle’s roof and responding to their slogans,” he said.

“Then I saw a thin, young man jumping toward her vehicle from the back and opening fire. Moments later, I saw her speeding vehicle going away,” he added.

Bhutto was rushed to the hospital and taken into emergency surgery. She died about an hour after the attack.

“At 6:16 p.m., she expired,” a member of Bhutto’s party who was at Rawalpindi General Hospital, Wasif Ali Khan, said.

“The surgeons confirmed that she has been martyred,” Bhutto’s lawyer, Babar Awan, said.

Bhutto’s supporters at the hospital exploded in anger, smashing the glass door at the main entrance of the emergency unit. Others burst into tears. One man with a flag of Bhutto’s Pakistan People’s Party tied around his head was beating his chest.

“I saw her with my own eyes sitting in a vehicle after addressing the rally. Then, I heard an explosion,” Tahir Mahmood, 55, said sobbing. “I am in shock. I cannot believe that she is dead.”

Many chanted slogans against Mr. Musharraf, accusing him of complicity in her killing.

“We repeatedly informed the government to provide her proper security and appropriate equipment … but they paid no heed to our requests,” Mr. Malik said.

As news of her death spread, angry supporters took to the streets in the northwestern city of Peshawar as well other areas, chanting slogans against Mr. Musharraf. In Rawalpindi, Bhutto’s supporters burned election posters from the ruling party and attacked police, who fled the scene.

In Karachi, shop owners quickly closed their businesses as supporters from Bhutto’s party burned tires on the roads.

Another former premier and opposition leader, Nawaz Sharif, arrived at the hospital and sat silently next to Bhutto’s body.

“Benazir Bhutto was also my sister, and I will be with you to take the revenge for her death,” he said. “Don’t feel alone. I am with you. We will take the revenge on the rulers.”

Speaking to the BBC, Mr. Sharif also questioned whether to hold the elections.

“I think perhaps none of us is inclined to think of the elections,” he said. “We would have to sit down and take a very serious look at the current situation together with the People’s Party and see what we have to do in the coming days.”

Hours earlier, four people were killed at a rally for Mr. Sharif when his supporters clashed with backers of Mr. Musharraf near Rawalpindi.

Bhutto’s death will leave a void at the top of her party, the largest political group in the country, as it heads into the parliamentary elections. It also fueled fears that the crucial vote could descend into violence.

Pakistan is considered a vital American ally in the fight against Al Qaeda and other Islamic extremists including the Taliban. Osama bin Laden and his inner circle are believed to be hiding in lawless northwest Pakistan along the border with Afghanistan.

In Washington, the State Department condemned the attack.

“It demonstrates that there are still those in Pakistan who want to subvert reconciliation and efforts to advance democracy,” a spokesman, Tom Casey, said.

America has for months been encouraging Mr. Musharraf to reach an accommodation with the opposition, particularly Bhutto, who was seen as having a wide base of support in Pakistan. Her party had been widely expected to do well in next month’s elections.

Educated at Harvard and Oxford universities, Bhutto served twice as Pakistan’s prime minister between 1988 and 1996. Her father, who also served as prime minister, was executed in 1979 two years after his ouster in a military coup.

Bhutto had returned to Pakistan from an eight-year exile on October 18. On the same day, she narrowly escaped injury when her homecoming parade in Karachi was targeted in a suicide attack that killed more than 140 people.

At the scene of today’s bombing, body parts and flesh were scattered at the back gate of the Liaqat Bagh park, where Bhutto had spoken. About 20 bodies were counted, including police, and many others were wounded.

Police cordoned off the street with white and red tape, and rescuers rushed to put victims in ambulances as people wailed nearby.

The clothing of some victims was shredded and people put party flags over their bodies. Police caps and shoes littered the asphalt.

Hundreds of riot police had manned security checkpoints around the venue. It was Bhutto’s first public meeting in Rawalpindi since she came back to the country.

In November, Bhutto had also planned a rally in the city, but Mr. Musharraf forced her to cancel it, citing security fears.

In recent weeks, suicide bombers have repeatedly targeted security forces in Rawalpindi, where Mr. Musharraf stays and the Pakistan army has its headquarters.