Bhutto's aides also said they doubted the militant commander Baitullah Mehsud was behind the attack and accused the government of a cover-up.

The dispute and conflicting reports about Bhutto's exact cause of death was expected to further enflame the violence wracking Pakistan two days after the popular former prime minister was killed in a suicide attack.

Roads across Bhutto's southern Sindh province were littered with burning vehicles as mobs of supporters continued their rampage. Factories, stores and restaurants were set ablaze in the city of Karachi, where 17 people have been killed and dozens injured, officials said.

Army, police and paramilitary troops patrolled the nearly deserted streets of Bhutto's home city of Larkana, where rioting left shops at a jewellery market smouldering.

Former Prime Minister Nawaz Sharif led a 47-member delegation of other opposition leaders to meet Bhutto's family to express condolences, said Sadiq ul-Farooq, spokesman for Sharif's party.

President Pervez Musharraf called Bhutto's husband, Asif Ali Zardari, promising to make every effort to bring the attackers to justice, state-run Pakistan Television reported.

The government blamed Bhutto's killing on al Qaida and Taliban militants operating with increasing impunity in the lawless tribal areas along the border with Afghanistan. It released a transcript Friday of a purported conversation between Mehsud and another militant, apparently discussing the assassination.

Interior Ministry spokesman Javed Iqbal Cheema described Mehsud as an al Qaida leader who was also behind the Karachi bomb blast in October against Bhutto that killed more than 140 people.