With the printing of ballot slips and the training of poll workers hampered, the commission has called an emergency meeting for Monday.
Fuelling the protests in Pakistan's streets is distrust of Pervez Musharraf, the president, and his administration's contention that Bhutto was killed by al-Qaeda.
Abu Bakr, a Bhutto supporter, told Al Jazeera: "This is a conspiracy. Musharraf has hatched this conspiracy. Al-Qaeda has not done this. This was a plot by Musharraf."
Streets in Karachi, where much of the violence has taken place, were generally quiet and deserted on Sunday morning, witnesses said.
But in eastern Pakistan, police said two suspected suicide bombers were killed when their device detonated prematurely. There were no other reported casualties.
The apparent target of the alleged attack in Haroonabad was Ijaz ul-Haq, a senior leader of the ruling Pakistan Muslim League-Q party and former religion minister.
Sohail Rahman, Al Jazeera' correspondent in Islamabad, said: "Ul-Haq was partially responsible, a part of the core group that made the decision to storm the Red Mosque in the capital in July."
Historically significant, Zia ul-Haq, his father, was the former military ruler who coincidentally ousted the then-prime minister Zulfikar Ali Bhutto, and had him executed in 1979.
Meanwhile, uncertainty has intensified over the circumstances of the assassination of Zulfikar's daughter.
The government claims that Bhutto died from a skull fracture caused by a blow to the head rather than an assassin's bullet.
Bhutto's Pakistan People's Party has dismissed the government statement, along with claims that she was killed by al-Qaeda, saying Musharraf's embattled administration was trying to cover up its failure to protect her.
Sherry Rahman, a PPP spokesperson, said: "This is dangerous nonsense. This is the government absolving itself from taking responsibility for the protection of a former prime minister, one who had been constantly asking for better protection."
Amateur photos, aired on Pakistani TV network Dawn News, have also emerged showing what appears to be a man aiming a gun at Bhutto alongside a white-swathed figure said to be the bomber.
Against such evidence, the government has said the exact cause of her death is not important.
Javed Iqbal Cheema, the interior ministry spokesman, said: "There is no doubt that the fires were shot, there is no doubt that there was a suicide bomber, there was an explosion.
"It doesn't suit the government, you know in no manner and in no way, whether she died of a bullet wound or whether she died of an explosion or because of some other cause."
The government spokesman also said it had no objection to carrying out an official post-mortem, although Bhutto's family rejected an autopsy.
Meanwhile, a spokesman for Baitullah Mehsud denied the government's claim that he was behind the assassination, saying: "We don't strike women."
In a recent interview with Al Jazeera in southern Waziristan, Mehsud, a tribal leader alleged to have links to al-Qaeda, said Musharraf is his prime enemy.
Mehsud said: "Our coalition seeks to fight the West in Afghanistan in an organised manner. However, the barbarism of the Pakistani military and its attacks on Muslims here in the tribal area has put our top priority the expulsion of the military from our areas."
A spokesman for Bhutto's party, Farhatullah Babar, said the government's accusation against Mehsud "appears to us to be a planted story, an incorrect story, because they want to divert the attention".
Without the charismatic Bhutto, her party is in disarray.
Bhutto's 19-year-old son, Bilawal, is to read her will on Sunday at the meeting in her home town of Naudero, but the Oxford law student is seen as too young to lead a dynasty whose history is entwined with that of Pakistan.
A party official said that if Bilawal were chosen, the party may set up an advisory council until he finishes school and is able to lead the party on a full-time basis.
|Asif Ali Zardani is a possible heir to his late|
wife's political party [AFP]
Sanam, Bhutto's younger sister, is also a possibility. The 50-year-old is the last surviving child of former premier Zulfiqar Ali Bhutto.
The choice of an immediate successor more likely lies between Makhdoom Amin Fahim, the PPP's vice-chairman and a long-time Bhutto aide, and Asif Ali Zardari, the former PM's husband.
While Zardari gained respect for enduring eight years in jail before being released without being convicted, political foes accuse him of corruption and some PPP loyalists blame him for tainting the Bhutto name.
When asked by the BBC on Saturday if he wanted to take over the party leadership, Bhutto's husband replied: "It depends on the party and it depends on the will."
Najam Sethi, editor of Pakistan's Daily Times, said: "Everybody in the party knows that they have to stick to the legacy of Bhutto and without that legacy, they are nobody.
He speculated Zardari would run the show to "keep the place warm for his son Bilawal, just like Congress party leader Sonia Gandhi is doing for her young son Rahul in India".
Sethi predicted the PPP would demand the establishment of a new national caretaker government and a reformed election commission for holding free and fair elections, a move that would likely see them delayed.