Bhutto's aides also said they doubted militant commander Baitullah Mehsud was behind the attack on the opposition leader and accused the government of a cover-up.
Meanwhile, attackers opened fire at a motorcade of Bhutto's supporters as they headed back to Karachi after her funeral, killing one man and wounding two others, said Waqar Mehdi, a spokesman for Bhutto's party. More than two dozen people have been killed nationwide since Thursday's assassination, officials said.
In Rawalpindi, thousands of Bhutto supporters spilled onto the streets after a prayer ceremony for her, throwing stones and clashing with police who fired tear gas to try and subdue the crowd.
President Pervez Musharraf told his top security officials that those looting and plundering "must be dealt with firmly and all measures be taken to ensure (the) safety and security of the people," the Associated Press of Pakistan reported.
Also Saturday, Pakistan's election commission called an emergency meeting for Monday to discuss the violence's impact on Jan. 8 parliamentary elections.
Nine election offices in Bhutto's home province of Sindh in the south were burned to the ground, along with voter rolls and ballot boxes, the commission said in a statement. The violence also hampered the printing of ballot papers, training of poll workers and other pre-election logistics, the statement said.
The U.S. government, which sees nuclear-armed Pakistan as a crucial ally in the war on terror, has pushed Musharraf to keep the election on track to promote stability, moderation and democracy in Pakistan, U.S. officials said.
Prime Minister Mohammedmian Soomro said Friday the government had no immediate plans to postpone the election, despite the violence and the decision by Nawaz Sharif, another opposition leader, to boycott the poll.
Bhutto's Pakistan Peoples Party also called a meeting Sunday to decide whether to participate in the vote. Her widower, Asif Ali Zardari, told the British Broadcasting Corp. that their son would read a message left by Bhutto and addressed to the party in event of her death.
On Saturday, roads across Bhutto's southern Sindh province were littered with burning vehicles, smoking reminders of the continuing chaos since her assassination Thursday. Factories, stores and restaurants were set ablaze in Pakistan's biggest city, 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 jewelry market smoldering.
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.