Enraged crowds rioted across Pakistan and hopes for democracy hung by a thread after Benazir Bhutto was gunned down Thursday as she waved to supporters from the sunroof of her armored vehicle.

The death of President Pervez Musharraf's most powerful opponent threw the nation into chaos just 12 days before elections, and threatened its already unsteady role as a key fighter against Islamic terror.

FOX Facts: Benazir Bhutto

Click here to view photos of Bhutto.

Click here to view photos of the blast (WARNING: GRAPHIC CONTENT).

The murder of Bhutto, one of Pakistan's most famous and enduring politicians, sparked violence that killed at least nine people and plunged efforts to restore democracy to this nuclear-armed U.S. ally into turmoil.

Another opposition politician, Nawaz Sharif, announced he was boycotting Jan. 8 parliamentary elections in which Bhutto was hoping to recapture the premiership, and Musharraf reportedly weighed canceling the poll.

Bhutto, 54, was struck down amid scenes of blood and chaos as an unknown gunman opened fire and, according to witnesses and police, blew himself up, killing 20 other people.

Musharraf blamed Islamic terrorists, pledging in a nationally televised speech that "we will not rest until we eliminate these terrorists and root them out."

President Bush, who spoke briefly by phone with Musharraf, looked tense as he spoke to reporters, denouncing the "murderous extremists who are trying to undermine Pakistan's democracy."

U.S. officials in Washington said they were trying to determine who might have carried out the attack.

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Bhutto's death marked yet another grim chapter in Pakistan's bloodstained history, 28 years after her father, Zulfiqar Ali Bhutto, another ex-prime minister, was hanged by a military dictatorship in the same northern city where she was killed.

Her death left her Pakistan People's Party leaderless and plunged the Muslim nation of 160 million into violence and recriminations, with Bhutto supporters accusing Musharraf's government of failing to protect her in the wake of death threats and previous attempts on her life.

As the news spread, supporters gathered at the hospital where Bhutto had been taken, smashed glass doors, stoned cars and chanted, "Killer, Killer, Musharraf."

At least nine people were killed in violence across the nation.

Musharraf called senior staff into an emergency meeting to discuss a response to the killing and whether to postpone the election, an Interior Ministry official said, speaking on condition of anonymity because of the sensitivity of the talks. Musharraf also announced three days of mourning for Bhutto, with all businesses, schools and banks to close.

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The killing appeared to shut off a possible avenue for a credible return to democracy after eight years under Musharraf's increasingly unpopular rule, and left a string of unanswered questions, chiefly whether it could strengthen Musharraf by eliminating a strong rival, or weaken him by sparking uncontrollable riots.

The U.S. was struggling to reformulate its plan to stabilize the country based on a rapprochement between Bhutto and Musharraf. Bhutto had returned in October after nearly a decade in exile hoping for a power-sharing deal with Musharraf, but had become his fierce critic, accusing elements in the ruling party of backing militants to kill her.

Pakistani analysts were plunged into gloom.

"This assassination is the most serious setback for democracy in Pakistan," said Rasul Baksh Rais, a political scientist at Lahore's University of Management Sciences. "It shows extremists are powerful enough to disrupt the democratic process."

Analyst Talat Masood, a retired general, said: "Conditions in the country have reached a point where it is too dangerous for political parties to operate."

Sharif, another former premier who now leads an opposition party, demanded Musharraf resign immediately and announced his party would boycott the elections, seen as vital to restoring democracy. He also called for the resignation of Musharraf, a former army chief who toppled Sharif in a 1999 coup.

"Musharraf is the cause of all the problems. The federation of Pakistan cannot remain intact in the presence of President Musharraf," he said.

Click to view international coverage of Bhutto's assassination

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Next to Musharraf, Bhutto was the best known political figure in the country, serving two terms as prime minister between 1988 and 1996. An instantly recognizable figure with graceful features under an ever-present head scarf, she bore the legacy of her hanged father and was respected in the West for her liberal outlook and determination to combat Islamic extremism.

It was a theme she had often returned to in recent campaign speeches.

Addressing more than 5,000 supporters Thursday in Rawalpindi, Bhutto dismissed the notion that Pakistan needed foreigners to help quell resurgent militants linked to the Taliban and Al Qaeda in the area bordering Afghanistan.

"Why should foreign troops come in? We can take care of this, I can take care of this, you can take care of this," she said.

As Bhutto left the rally in a white SUV, youths chanted her name and supportive slogans, said Sardar Qamar Hayyat, an official from Bhutto's party who was about 10 yards away.

Despite the danger of physical exposure, a smiling Bhutto stuck her head out of the sunroof and responded, 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. That was the time when I heard a blast and fell down," he said.

Bhutto was rushed into surgery. A doctor on the surgical team said a bullet in the back of her neck damaged her spinal cord before exiting from the side of her head. Another bullet pierced the back of her shoulder and came out through her chest, he said on condition of anonymity because he was not authorized to speak to the media. She was given an open-heart massage, but the spinal cord damage was too great, he said.

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

Hours later, supporters carried Bhutto's body out of the hospital in a plain wooden coffin and sent it for burial in her ancestral home near the southern city of Larkana.

Bhutto, who was married with three children, had returned to Pakistan from nearly a decade in exile on Oct. 18, and her homecoming parade in Karachi was also targeted by a suicide attacker, who killed more than 140 people. She narrowly escaped injury.

Rawalpindi, a former capital, has a history of political violence. The park where Bhutto made her last speech is the same one where the country's first prime minister, Liaquat Ali Khan, was shot to death in 1951. It is named after him.

Musharraf survived two bombing attacks here in 2003. Earlier that year, Khalid Shaikh Mohammed, alleged mastermind of the 9/11 attacks, was captured in Rawalpindi. In recent weeks, suicide bombers have repeatedly targeted security forces in the city.

Bhutto's father was hanged in 1979 in Rawalpindi on charges of conspiracy to murder -- an execution that led to violent protests across the country similar to those that raged Thursday.

Thursday's rally was Bhutto's first since returning to Pakistan, Musharraf having forced her to scrap a meeting here last month citing security fears. Hundreds of riot police manned security checkpoints at the park.

Afghan President Hamid Karzai, who met with Bhutto just hours before her death, called her a brave woman with a clear vision "for her own country, for Afghanistan and for the region -- a vision of democracy and prosperity and peace."

Rep. Patrick Kennedy, D-R.I., visiting Pakistan with Sen. Arlen Specter, R-Pa., said he was just leaving his hotel room for dinner with Bhutto at her home when he got the news.

"I couldn't believe it," he told The Associated Press by phone. "Her death really dashed the hope of many here in Pakistan and that's why there's so much disillusionment and anger being vented through these protests that are lighting up the sky tonight as people set fires all over the countryside."

U.S. intelligence agencies said it was to soon to say who carried out the attack.

FBI spokesman Richard Kolko said the agency "continues to work with our U.S. intelligence community partners reviewing the Al Qaeda claims for responsibility for any intelligence value. The validity of those claims are undetermined."

Video: Click here to watch Greta Van Susteren's interview with Bhutto.

Video: Bhutto Killed in Attack

The statement came after a law enforcement official told the AP that a national FBI and Homeland Security bulletin to law enforcement agencies cited Islamist Web sites as saying al-Qaida had claimed responsibility. The official asked to remain anonymous because he was not authorized to speak publicly about it.

Director of National Intelligence spokesman Ross Feinstein said his agency was "in no position right now to confirm who may have been responsible."

One man was killed in a shootout between police and protesters in Tando Allahyar, a town 120 miles north of Karachi, Pakistan's commercial hub, said Mayor Kanwar Naveed. Four others were killed in Karachi, two were killed elsewhere in southern Sindh province and two in Lahore, police said.

Karachi shopkeepers quickly shuttered their stores as protesters burned vehicles, a gas station and tires on the roads, said Fayyaz Leghri, a local police official. Gunmen shot and wounded two police officers, he said.

Bhutto's supporters in many towns burned banks, shops and state-run grocery stores. Some torched ruling party election offices, according to Pakistani media.

Authorities will deploy troops to stop violence if needed, said Akhtar Zamin, home minister for Sindh province.

The U.N. Security Council vigorously denounced the killing and urged "all Pakistanis to exercise restraint and maintain stability in the country."