~ Questions about Bhutto's assassination have intensified since she died Thursday evening.

ISLAMABAD, Pakistan -- Pakistan rejected foreign help in investigating the assassination of Benazir Bhutto on Saturday, despite controversy over the circumstances of her death and three days of paralyzing turmoil.

The Islamic militant group blamed by officials for the attack that killed Bhutto denied any links to the killing Saturday, and Bhutto's aides accused the government of a cover-up.

President Pervez Musharraf ordered his security chiefs to quell rioting by Bhutto's grieving followers that has resulted in the deaths of at least 44 people over three days and caused tens of millions of dollars in damage.

"Criminals should stop their despicable activities, otherwise they will have to face serious consequences," Interior Ministry spokesman Javed Iqbal Cheema said.

Bhutto's Pakistan People's Party called a meeting Sunday at which they are expected to choose a new leader, decide whether to participate in Jan. 8 parliamentary elections and hear her last will and testament.

If the party pulls out, it would destroy the credibility of the poll, already being boycotted by rival opposition leader Nawaz Sharif. The U.S. government has pressured Musharraf, who seized power in a coup eight years ago, to push ahead with the election to promote stability in this nuclear armed nation, a key ally against Islamic extremism.

The riots destroyed nine election offices -- along with the voter rolls and ballot boxes inside, the election commission said. The commission has called an emergency meeting for Monday to decide how to proceed.

Questions about Bhutto's assassination have intensified since she died Thursday evening when a suicide attacker shot at her and then blew himself up as she waved to supporters from the sunroof of her armored vehicle outside a campaign rally.

The disputes were sure to further enflame the violence and have led to calls for an international, independent investigation into the attack.

Democratic presidential candidate Hillary Rodham Clinton said Friday that an international probe was vital because there was "no reason to trust the Pakistani government," while others called for a U.N. investigation.

Cheema dismissed the suggestion. "This is not an ordinary criminal matter in which we require assistance of the international community. I think we are capable of handling it," he said. An independent judicial investigation should be completed within seven days of the appointment of its presiding judge, he said.

White House spokesman Tony Fratto said Pakistan had not asked the United States for help.

"It's a responsibility of the government of Pakistan to ensure that the investigation is thorough. If Pakistani authorities ask for assistance, we would review the request," he said.

British Foreign Secretary David Miliband offered his country's assistance. "Obviously it's very important that a full investigation does take place, and has the confidence of all concerned," he said.

The government blamed the attack on Baitullah Mehsud, head of the Tehrik-i-Taliban, a newly formed coalition of Islamic militants along the Afghan border believed to be linked to al-Qaida and committed to waging holy war against the government.

But a spokesman for Mehsud, Maulana Mohammed Umer, dismissed the allegations as "government propaganda."

"We strongly deny it. Baitullah Mehsud is not involved in the killing of Benazir Bhutto," he said in a telephone call he made to The Associated Press from the tribal region of South Waziristan. "The fact is that we are only against America, and we don't consider political leaders of Pakistan our enemy."

Bhutto's aides said they, too, doubted Mehsud was involved and accused the government of a cover-up.

"The story that al-Qaida or Baitullah Mehsud did it appears to us to be a planted story, an incorrect story, because they want to divert the attention," said Farhatullah Babar, a spokesman for Bhutto's party.

After an October suicide attack targeted her in the city of Karachi, Bhutto accused elements in the ruling party of plotting to kill her. The government denied the claims, and Babar said Bhutto's allegations were never investigated.

Authorities initially said Bhutto died from bullet wounds. A surgeon who treated her later said the impact from shrapnel on her skull killed her.

But Cheema said Friday that Bhutto was killed when the shockwaves from the bomb smashed her head into the sunroof as she tried to duck back inside the vehicle.

Bhutto's spokeswoman Sherry Rehman, who was in the vehicle that rushed her boss to the hospital, disputed that.

"She was bleeding profusely, as she had received a bullet wound in her neck. My car was full of blood. Three doctors at the hospital told us that she had received bullet wounds. I was among the people who gave her a final bath. We saw a bullet wound in the back of her neck," she said. "What the government is saying is actually dangerous and nonsensical. They are pouring salt on our wounds. There are no findings, they are just lying."

Cheema stood by the government's version of events, and said Bhutto's party was free to exhume her body for an autopsy.

Roads across Bhutto's southern Sindh province were littered with burning vehicles, smoking reminders of the continuing chaos raging across the country. Business centers, gas stations and schools remained closed and many roads were deserted.

Desperate to quell the violence, the government sent troops into several cities. Soldiers patrolled some Karachi neighborhoods Saturday, and residents complained of shortages of food and gasoline.

One gunbattle in Karachi killed three people and wounded 17 others in a neighborhood where rioters had looted food stores in recent days, police officer Fayyaz Khan said.

Rangers were given the authority to shoot at rioters, and some of the wounded in Karachi said the paramilitary troops fired without provocation.

Najib Ullah, 13, said he was among 15 boys playing cricket in the street when he was hit by a ranger bullet. He said he saw other boys falling to the ground, apparently after being shot.

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AP reporters Zarar Khan in Larkana, Sadaqat Jan and Munir Ahmad in Islamabad, Ishtiaq Mahsud in Dera Ismail Khan and Afzal Nadeem and Ashraf Khan in Karachi contributed to this report.