Two blasts rocked Karachi, the country's largest city, as hundreds of thousands of people lined the streets to greet the motorcade of Bhutto, who flew in from Dubai after eight years of self-imposed exile.
Police believe the attack, one of the bloodiest in Pakistan's history, was perpetrated by suicide bombers. President General Pervez Musharraf condemned the violence as a "conspiracy against democracy.'
The ex-premier, who sustained minor injuries in the blasts, pledged a day before her arrival to put an end to extremism and to develop democracy in the country if she returns to power. Speaking at a news conference in Dubai, she confirmed her intention to run in the parliamentary elections slated for January next year.
She said she had received threats from militants, but that: "Muslims know that if they attack a woman they will burn in hell." Extra police reinforcements and bomb disposal experts were deployed from other parts of the country to provide protection against threats of suicide attacks by militants.
The head of the center-left Pakistan People's Party (PPP), Bhutto served as Pakistan's prime minister on two separate occasions and is expected to bid for a third premiership, but both her previous governments were brought down amid corruption allegations and she was forced to flee in 1999, dismissing the allegations as politically motivated.
President Musharraf has declared an amnesty for Bhutto to protect her against the corruption charges, but the Pakistani Supreme Court is set to hear appeals against the amnesty.
Benazir Bhutto is the daughter of deposed premier Zulfikar Ali Bhutto, the founder of the PPP, who served as the president of Pakistan between 1971 and 1973, and as prime minister between 1973 and 1977. He was hanged in 1979 by the country's then military ruler, General Muhammad Zia-ul-Haq, allegedly for sanctioning the assassination of a political opponent.