Former Pakistani Prime Minister Benazir Bhutto was killed in an apparent suicide bombing in the military garrison town of Rawalpindi, according to her aides, throwing Pakistan's political system into a new round of turmoil.

Ms. Bhutto was emerging from a political rally in Rawalpindi when an attacker fired shots and detonated himself, according to news reports from Pakistan. At least a dozen people are believed dead from the blast.

  
Rescue workers and volunteers carry an injured man after a suicide attack on Bhutto's rally.
"At 6:16 p.m. she expired," Wasif Ali Khan, a member of Ms. Bhutto's Pakistan People's Party, told the Associated Press. He spoke from the Rawalpindi General Hospital where the former prime minister was taken after the attack.

Supporters of Ms. Bhutto already were gathering outside the hospital, with some blaming Pakistan President Pervez Musharraf for their leader's death. "Dog, Musharraf, dog,'' some shouted, while throwing rocks at the hospital's windows, according to the AP.

Ms. Bhutto was seen as the front-runner to become Pakistan's next prime minister in elections scheduled for next month. And her death now undermines an emerging political alliance that appeared to be emerging between herself as the possible next prime minister, Mr. Musharraf as president, and Gen. Ashfaq Kiyani as the head of the Pakistani military.

Ms. Bhutto and Mr. Musharraf had a contentious relationship, but there were growing hopes in Washington that the two could set aside their differences and help stabilize Pakistan's fractious political system. Though rivals, both are secular, moderate leaders, who have agreed that Pakistan needs to intensify its fight against Islamic extremism.

New Framework

In recent days, many senior Bush administration officials were expressing optimism in the direction Pakistan was taking politically, banking on the power-sharing relationship emerging between Ms. Bhutto, Mr. Musharraf and Gen. Kiyani. "There could have been worse outcomes then this," a senior Bush administration official said about the emerging alliance before her death.

Now the U.S. is expected to have to work with Mr. Musharraf to shape a new political framework for Pakistan. There's also the expectation that Ms. Bhutto's assassination could renew calls by Mr. Musharraf for a restoration of emergency rule, which he lifted only days ago.

Ms. Bhutto ran her political party, known as the PPP, in a very top-down manner. Many reformists in Islamabad and Washington claimed she structured it simply as  a feudal vehicle to advance the interests of herself and family.

Ms. Bhutto's father, Zulfikar Ali Bhutto, served as Pakistan's prime minister in the 1970s before the Pakistani military hanged him on treason charges. Ms. Bhutto's mother, siblings and husband have also all played major roles in the PPP.

It's unclear who will now take the mantle of the PPP and possibly run for prime minister in Ms. Bhutto's place. During her exile, a new generation of PPP leadership was emerging. But there have been charges that Ms. Bhutto marginalized these new voices upon her return.

Mr. Musharraf will face enormous new challenges as a result of Ms. Bhutto's death. Already, PPP supporters were claiming Pakistan's president and his security services were complicit in the murder, citing its occurrence near the military's headquarters in Rawalpindi. And Mr. Musharraf could face another round of popular protests challenging his rule.

Nawaz Sharif, another former prime minister who recently returned to Pakistan, has also launched a protest movement challenging Mr. Musharraf's rule. A Pakistani court barred Mr. Sharif from competing in the January election, citing corruption charges outstanding against him. But Ms. Bhutto's death could increase pressure on Mr. Musharraf to allow Mr. Sharif to run.

Met With Karzai

Before the rally, Ms. Bhutto had met with visiting Afghan President Hamid Karzai at the end of his two-day visit here and told him that if she is elected prime minister she will work with him to fight terror. "We, too, believe that it is essential for both of our countries, and indeed the larger Muslim world, to work to protect the interest of Islamic civilization by eliminating extremism and terrorism," she said after their meeting.

The attack at the Bhutto rally took place just miles from the site of a clash earlier in the day between government party supporters and backers of Mr. Sharif that killed four people and wounded three.

Sadiq ul-Farooq, a spokesman for Mr. Sharif's party, said the opposition-party leader was about 1.3 miles away when pro-government party supporters opened fire on people gathering for a rally at Karal Chowk, near the airport about 10 miles outside Islamabad.

"Nawaz Sharif and his procession are safe, but we have received reports that a few people were wounded and maybe a few suffered fatal injuries," Mr. ul-Farooq said. All the injured were from Mr. Sharif's Pakistan Muslim League-N group.

Pakistan's private ARY news channel quoted Mr. Sharif as saying the government had deliberately not provided security to his backers.

Imtiaz Ranjha, a spokesman for the ruling Pakistan Muslim League-Q party, condemned the attack and accused Mr. Sharif's supporters of provoking the fight. The party called for those involved to be punished, he said.

The violence came as the campaign for the parliamentary elections gathered momentum after eight years of military rule under recently retired army chief Musharraf. Opposition leaders are already claiming the election will be rigged against them, which authorities deny.