( AFP ) - Prime Minister Gordon Brown said Benazir Bhutto was killed by "cowards afraid of democracy" Thursday as he led tributes to the slain politician in Britain, where she studied and spent part of her exile.
Brown said Bhutto's death was "a sad day for democracy" and "a tragic hour for Pakistan".
He said Bhutto was a "woman of immense personal courage and bravery".
"She risked everything in her attempt to win democracy in Pakistan and she has been assasinated by cowards afraid of democracy," Brown said.
"This atrocity strengthens our resolve that terrorists will not win there, here or anywhere in the world."
Foreign Secretary David Miliband called for "restraint but also unity" following her assassination after a rally in Rawalpindi.
Opposition politicians in Britain also condemned the killing.
"This is an appalling act of terrorism," said Conservative leader David Cameron. "Today Pakistan has lost one of its bravest daughters.
"Those responsible have not only murdered a courageous leader but have put at risk hopes for the country's return to democracy."
Nick Clegg, the newly-elected leader of the Liberal Democrats, added: "Her tragic death is a hammer blow against the dream of pluralism and tolerance in modern day Pakistan."
Bhutto studied at Oxford University and spent some time in London, where she had a home, during an eight-year self-imposed exile which ended with her return to Pakistan in October.
She also had a strong following among the hundreds of thousands of British residents who still have ties to Pakistan.
Bhutto's friends in Britain, including some in high public office, were stunned by the death and expressed fears for Pakistan's future.
Justice Secretary Jack Straw described her as "a personal friend".
"Benazir comes from an extraordinary political dynasty in Pakistan, a dynasty which has been all too acquainted with tragedy," he said.
"She will be sorely missed."
Bishop of Rochester Michael Nazir-Ali, a senior figure in the Anglican Church, also counted her as a friend and said her death "raises serious questions about the government's ability to provide security for its citizens".
Rehman Christi, a former aide and family friend of Bhutto, remembered her as among the "brightest politicians in Pakistan's history who offered the masses hope and inspiration", in an interview with Sky News television.
He added that she had left a letter with Pakistani President Pervez Musharraf and the Foreign Office in London naming three individuals who "posed a risk to her safety".
"She knew the risks but her country needed her, she needed to go back to bring stability to Pakistan," he said.
"She knew there were risks but for the greater good of the country she went back to Pakistan and now has paid for that with her life."
Munib Anwar, a member of the Pakistan Lawyers' Action Committee pressure group, wept as he said it was "a very sad day" for Pakistan.
"She was such a brave woman. The hopes for a democratic Pakistan have been dashed today," he said.
"She was the one great hope for Pakistan. Where are we now?
"I do not have any hope for the future."
Amit Roy, a writer and political commentator who was a friend of Bhutto, said that in one of his last conversations with her, he had joked that she should leave politics and become an academic.
"But she felt that it was always her ambition to return to Pakistan as prime minister. She knew the risks but was determined to stay," he said.
"The elections should go ahead but they might have to be postponed for a while because emotions will be running very high.
"It might be logistically impossible to have them at the moment."