Supporters of Pakistan's former Prime Minister Benazir Bhutto mourn their leader's death during Bhutto's burial at her ancestral graveyard Friday in Garhi Khuda Bakhsh near Larkana, Pakistan. Bhutto was killed along with 20 others on Thursday in a suicide attack.

Islamabad, Pakistan ? Pakistan’s government asserted Friday that al-Qaida was behind the assassination of Benazir Bhutto, and offered the transcript of a conversation as proof. Hundreds of thousands mobbed her funeral as the army tried to quell rioting across the nation that left 27 dead.

President Pervez Musharraf’s government also said Bhutto was not killed by gunshots or shrapnel as originally claimed. Instead, it said her skull was shattered by the force of a suicide bomb blast that slammed her against a lever in her car’s sunroof.

The new explanations were part of a rapidly evolving political crisis triggered by the death of Bhutto, Musharraf’s most powerful foe in the elections. The rioting by Bhutto’s furious supporters raised concerns that this nuclear-armed nation, plagued by chaos and the growing threat from Islamic militants even before the killing, was in danger of spinning out of control.

Pentagon officials said Friday they have seen nothing to give them any worries about the security of Pakistan’s nuclear arsenal.

While many grieving Pakistanis turned to violence, hundreds of thousands paid their last respects to the popular opposition leader as she was placed beside her father in a marble mausoleum in the Bhutto ancestral village in southern Sindh province.

“I don’t know what will happen to the country now,” said mourner Nazakat Soomro, 32.

The government said it would hunt down those responsible for her death in the lawless tribal areas along the Afghan border where Osama bin Laden and other al-Qaida leaders are thought to be hiding.

“They will definitely be brought to justice,” Interior Ministry spokesman Javed Iqbal Cheema said.

The government released a transcript Friday of a purported conversation between militant leader Baitullah Mehsud and another militant.

“It was a spectacular job. They were very brave boys who killed her,” Mehsud said, according to the transcript. The government did not release an audiotape.

Cheema described Mehsud as an al-Qaida leader who was also behind most other recent terror attacks in Pakistan, including the Karachi bomb blast in October against Bhutto that killed more than 140 people.

Mehsud is thought to be the commander of pro-Taliban forces in the tribal region of South Waziristan, where al-Qaida fighters are also active.

In the transcript, Mehsud gives his location as Makin, a town in South Waziristan.

This fall, he was quoted in a Pakistani newspaper as saying that he would welcome Bhutto’s return from exile with suicide bombers. Mehsud later denied that in statements to local television and newspaper reporters.

There have been no reports of reliable claims of responsibility by al-Qaida.

Cheema announced the formation of two inquiries into Bhutto’s death, one to be carried out by a high court judge and another by security forces. Bhutto was assassinated Thursday evening after a rally in the garrison city of Rawalpindi near Islamabad. Twenty other people also died in the attack.

On Thursday, authorities had said Bhutto died from bullet wounds fired by a young man who then blew himself up. A surgeon who treated her, however, said Friday she died from the impact of shrapnel on her skull.

But later Friday, Cheema said those two accounts were mistaken. He said all three shots missed her as she greeted supporters through the sunroof of her vehicle, which was bulletproof and bombproof.

He also denied that shrapnel caused her death, saying Bhutto was killed when she tried to duck back into the vehicle, and that the shock waves from the blast knocked her head into a lever attached to the sunroof, fracturing her skull. The government released a photograph showing blood on the lever.

Denying charges the government failed to give her adequate security protection, Cheema said it was Bhutto who made herself vulnerable and pointed out that the other passengers inside Bhutto’s bombproof vehicle were fine.

“I wish she had not come out of the rooftop of her vehicle,” he said.

Bhutto’s death sparked deadly rioting that killed at least 27 people, according to an Interior Ministry official who spoke on condition of anonymity because he was not authorized to speak to the media.