On the day she was killed, Benazir Bhutto was planning to give two U.S. lawmakers a 160-page dossier accusing the government of rigging upcoming elections, one of her aides said Tuesday, as calls for an international probe into her death intensified.

Anger at the assassination of the popular opposition leader sparked days of rioting across the country that election officials said would almost certainly force them to delay the Jan. 8 polls. A final decision on a postponement, which could incite more opposition protests, was expected Wednesday.

Bhutto was killed Thursday evening in a shooting and bombing attack on her vehicle as she left a campaign rally. She had been scheduled to meet hours later with U.S. Sen. Arlen Specter of Pennsylvania and U.S. Rep. Patrick Kennedy of Rhode Island.

Sen. Latif Khosa, a lawmaker from Bhutto's Pakistan Peoples Party, said she had planned to give the lawmakers a report outlining complaints on "pre-poll rigging" by President Pervez Musharraf's government and the military-run Inter-Services Intelligence Directorate.

Khosa said he did not know if Bhutto's killing was linked to her plans to release the document. Officials at the Information Ministry and the Interior Ministry declined to immediately comment. The government has previously denied charges of vote rigging and said it had nothing to do with Bhutto's death.

The dossier outlined several instances of electoral interference, including one case where an officer from the intelligence services sat nearby as an election official rejected nomination papers from opposition candidates, Khosa said. Another official stopped a candidate from filing his nomination in the southwestern Baluchistan province, said Khosa, who wrote the report as head of the party's election team.

"The elections were to be thoroughly rigged, and the king's party was to benefit in the electoral process," he said, referring to the pro-Musharraf Pakistan Muslim League-Q.

The evidence was based on complaints by party candidates and information from sources in the security services, he said.

Despite accusing the government of rigging the vote, Bhutto had rejected calls for a boycott, saying she did not want leave the field open for Musharraf's loyalists.

Since Bhutto's slaying, the government has come under harsh criticism for its security arrangements for the candidate, its claim that an Islamic militant was behind her death and its conclusion that it was the force of the blast and not gunshot wounds that killed her.

Her husband, Asif Ali Zardari, has led calls for an international, independent investigation into the attack.

"I hope the government will agree to our demand for foreign investigators to probe the assassination of Benazir Bhutto," he said. "If they avoid it, we will directly approach the world powers in this regard."

The government said in a statement it was "committed to a thorough and transparent investigation and will not shy away from receiving assistance from outside, if needed."

U.S. officials said the United States had quietly joined calls for international experts to join the probe and expected investigators from Britain's Scotland Yard to play a significant role.

As part of the investigation, the government took out newspaper ads offering a 10 million rupee (US$162,000, euro111,000) reward for information about her killers. The ad shows a fuzzy still frame from a video featuring the presumed shooter and bomber seconds before the attack, and a photograph of the bomber's severed head.

Bhutto's killing thrust the country into crisis and triggered nationwide riots that killed 58 people and caused tens of millions of dollars in damage. Bhutto's home province of Sindh was especially hard hit.

Though the violence has died down since Sunday — amid a heavy police and army presence — Election Commission spokesman Kanwar Dilshad said it now "looks impossible" to hold the polls Jan. 8.

"Our offices in 10 districts of Sindh have been burned, the electoral rolls have been burned, the polling schemes, the nomination papers have been burned," he said. "We are in a very tricky situation."

The commission said it would meet with Pakistan's political parties before announcing a decision Wednesday.

The polls are seen as crucial to restoring democracy to this nuclear-armed U.S. ally in the wake of a six-week state of emergency Musharraf declared in November.

Opposition groups have demanded the elections proceed on time, and Nawaz Sharif, leader of another opposition party, threatened street protests if they were postponed.

Bhutto's party, certain to win sympathy votes in a quick poll, accused Musharraf of wanting a delay to allow anger over her death to evaporate.

"There have been elections in conflict zones such as Iraq and Afghanistan so I find it difficult to understand why this election cannot be held on time," Sherry Rehman, a spokeswoman for Bhutto's party, told Dawn News TV.

Britain and the United States were also eager for the vote to take place as scheduled, but have indicated they would accept a slight delay.