In India, which has fought three wars against Pakistan, Prime Minister Manmohan Singh said Bhutto is irreplaceable, and noted she had striven to improve relations between the two nuclear-armed countries.

"I was deeply shocked and horrified to hear of the heinous assassination," Singh said. "In her death, the subcontinent has lost an outstanding leader who worked for democracy and reconciliation in her country."

Afghanistan's President Hamid Karzai, who met Bhutto earlier on Thursday in Islamabad, said he was "deeply pained" by the assassination of "this brave sister of ours, a brave daughter of the Muslim world"

"She sacrificed her life, for the sake of Pakistan and for the sake of this region," he said. "I found in her this morning a lot of love and desire for peace in Afghanistan, for prosperity in Afghanistan and ... Pakistan."

In a letter to Pakistani President Pervez Musharraf, French President Nicolas Sarkozy called the attack an "odious act" and said "terrorism and violence have no place in the democratic debate and the combat of ideas and programs."

Bhutto, a former two-time prime minister of Pakistan, was killed in a suicide attack in Rawalpindi just 10 weeks after she returned to her homeland from eight years in exile. A suicide attack on her homecoming parade killed more than 140 people. The articulate, poised 54-year-old had lashed out at the spread of Islamic extremism as she campaigned for next month's parliamentary elections.

The United States had been at the forefront of foreign powers trying to arrange reconciliation between Bhutto and Musharraf, who under heavy U.S. pressure resigned as army chief and earlier this month lifted a state of emergency, in the hope it would put Pakistan back on the road to democracy.

President Bush demanded that the killers be brought to justice.

"The United States strongly condemns this cowardly act by murderous extremists who are trying to undermine Pakistan's democracy," he said. He expressed his deepest condolences to Bhutto's family and to the families of others slain in the attack and to all the people of Pakistan.

U.N. Secretary General Ban Ki-moon also called for the perpetrators to be brought to justice and for "all Pakistanis to work together for peace and national unity."

The Vatican spokesman, the Rev. Federico Lombardi, said Pope Benedict XVI was immediately informed of the "terrible news."

"One cannot see signs of peace in this tormented region," Lombardi said.

Sarkozy said Bhutto had paid "with her life her commitment to the service of her fellow citizens and to Pakistan's political life" and urged Pakistan's elections be held as scheduled on Jan. 8.

In Britain, where Bhutto had attended Oxford University, Prime Minister Gordon Brown said she "risked everything in her attempt to win democracy in Pakistan and she has been assassinated by cowards who are afraid of democracy."

"The terrorists must not be allowed to kill democracy in Pakistan, and this atrocity strengthens our resolve that the terrorists will not win there, here, or anywhere in the world," Brown said.

Italian Premier Romano Prodi said he was filled with grief and called Bhutto "a woman who chose to fight her battle until the end with a single weapon — the one of dialogue and political debate."

"The difficult path toward peace and democracy in that region must not be stopped, and Bhutto's sacrifice will serve as the strongest example for those who do not surrender to terrorism," Prodi said.

Chilean President Michelle Bachelet, during a speech south of Santiago, paid "sincere tribute to a woman ... who fought her entire life for a better Pakistan."

German Chancellor Angela Merkel said the "cowardly terrorist attack ... also targets the stability and democratic process of Pakistan."

In Moscow, Anatoly Safonov, Russian President Vladmir Putin's envoy on international cooperation against terrorism, expressed fears the assassination would trigger violent repercussions.

"The already unstable situation in Pakistan will be further exacerbated by this powerful factor," Safonov said, according to the Interfax news agency.

Russian Foreign Ministry spokesman Mikhail Kamynin condemned the attack, the RIA-Novosti news agency reported.

"We hope that the leadership of Pakistan will succeed in taking all measures for guaranteeing security in the country," Kamynin said.

French Foreign Minister Bernard Kouchner, who personally knew Bhutto, said he hails her memory and called on the international community to support Pakistan and its democracy.

Sweden's Foreign Minister Carl Bildt said he had felt disgust when receiving the news of Bhutto's murder, which he called "bestial."

"I feel a strong worry for the consequences this will have for Pakistan," he said.