World leaders have voiced outrage at Benazir Bhutto's assassination and have expressed fears for the fate of the nuclear-armed state.
US president George W Bush condemned the killing as a "cowardly act" and urged Pakistanis to press ahead with a planned national election. Russia's top Asia diplomat said the assassination would "trigger a wave of terrorism".
French president Nicolas Sarkozy called it odious. "France, like the European Union, is particularly attached to stability and democracy in Pakistan," he said in a letter to Pakistan's president Pervez Musharraf.
"The subcontinent has lost an outstanding leader who worked for democracy and reconciliation in her country," said prime minister Manmohan Singh of India, Pakistan's giant neighbour and nuclear rival. "The manner of her going is a reminder of the common dangers that our region faces from cowardly acts of terrorism and of the need to eradicate this dangerous threat."
Mr Bush urged Pakistanis to honour Ms Bhutto's memory by continuing with the democratic process and said those behind the attack must be brought to justice.
"The United States strongly condemns this cowardly act by murderous extremists who are trying to undermine Pakistan's democracy," he told reporters at his Texas ranch.
British prime minister Gordon Brown said Ms Bhutto had risked everything to try and bring democracy to her country.
UN secretary-general Ban Ki- moon said the assassination was a "heinous crime" and an "assault on stability" in Pakistan.
José Manuel Barroso, president of the European Commission, said it was "an attack against democracy and against Pakistan".
"It is a criminal act and is strongly condemned," Iranian foreign ministry spokesman Mohammad Ali Hosseini said. "Pakistan strongly needs calmness and the return of stability."
A Vatican spokesman said Pope Benedict had been told, adding: "It is difficult to see any glimmer of hope, peace, reconciliation in this country."