An explosion outside a rally for Pakistani opposition leader Benazir Bhutto has killed at least 20 people, witnesses said. Police said the bombing was a suicide attack. An aide to Bhutto says the politician is unharmed.

Ex-Pakistan Prime Minister Benazir Bhutto has died, according to media reports.

Former Pakistani prime minister Benazir Bhutto was assassinated Thursday at a political rally, two months after she returned from eight years of exile to attempt a political comeback, officials said.

Bhutto was shot at close range as she was leaving the rally in this garrison city south of Islamabad, aides said. Immediately after the shooting, a suicide bomber detonated explosives near Bhutto's car, killing at least 15 other people.

Bhutto was rushed to a hospital with extensive wounds to her torso, her supporters said. Shortly after she arrived at the hospital, an official came out of the building and told a crowd of supporters Bhutto was dead.

A party security adviser said Bhutto was shot in the neck and chest as she got into her vehicle, then the gunman blew himself up.

Sky News correspondent Alex Crawford said from Pakistan the country's upcoming January elections would "most likely be postponed or canceled" because of the attack.

"The entire political scene in Pakistan will be torn apart. She will become a martyr in many people's eyes."

"This is an end of a dream for them."

An obscure Italian Web site said Mustafa Abu al-Yazid, al Qaeda's commander in Afghanistan, told its reporter in a phone call, "We terminated the most precious American asset which vowed to defeat [the] mujahedeen."

It said the decision to assassinate Bhutto was made by al Qaeda's No. 2 leader, Ayman al Zawahri in October. Before joining Osama bin Laden in Afghanistan, Zawahri was imprisoned in Egypt for his role in the assassination of then-Egyptian President Anwar Sadat.

"She openly threatened al Qaeda, and she had American support," said ABC News consultant Richard Clarke, the former White House counterterrorism adviser. "If al Qaeda could try to kill Musharraf twice, it could easily do this," he said.

Al Qaeda had claimed responsibility for the bomb attack Oct. 18 during Bhutto's homecoming rally that killed 140 people but left the former prime minister uninjured.

Democratic New Mexico Gov. Bill Richardson, a former U.S. ambassador to the United Nations, called on President Bush to force Musharraf to step down. Until then, Richardson said the U.S. must suspend military aid to the Pakistani government.

"A leader has died, but democracy must live. The United States government cannot stand by and allow Pakistan's return to democracy to be derailed or delayed by violence," Richardson said.