"I know exactly who wants to kill me," she told the French magazine, Paris-Match.
"They are dignitaries of General Zia's former regime who are behind extremism and fanaticism."
Nobody has so far claimed responsibility for one of Pakistan's deadliest bombings, which killed at least 136 people and injured 290.
In a press conference in Karachi, Ms Bhutto said she had not wanted all her top party leadership to travel in her truck as "I knew" there might be an assassination attempt.
Ms Bhutto, who praised those who died while protecting her as heroes, said she did not blame the government for the attack but called for an inquiry as to why street lights had been switched off during her procession.
"If the street lights had been on," she said "We would have spotted the suicide bombers... The guards had floodlights on but it was difficult to scan the crowds as there were so many people".
Denouncing her would-be assassins as trying to destroy Pakistan and of damaging Islam, she said: "It is against our religion to kill innocent people".
The Pakistani government has blamed Islamist militants for the assassination attempt and police are focusing on militants linked to the Taliban and al-Qaida based in tribal regions bordering Afghanistan, where they have stepped up attacks on Pakistani troops.
But Ms Bhutto pointed to the Pakistan's powerful intelligence services, the ISI.
General Zia seized power in a coup against Ms Bhutto's father, Zulfikar Ali Bhutto, in 1977. The general, who died in a mysterious plane crash in 1988, had Mr Bhutto tried on trumped-up charges and executed.
"We have to purge elements still present in our services," she said. "Many went into retirement and then were taken back. Today they hold much power. For them I represent a danger: if I bring back democracy to the country, they will lose influence".
The Pakistani president, General Pervez Musharraf, said he was "deeply shocked" by the attack and condemned it "in the strongest possible words".
Gen Musharraf, who has survived several assassination attempts, appealed for calm and promised an exhaustive investigation and severe punishment for those responsible.
Well before Ms Bhutto's return, threats had been made against her. Two weeks ago, Baitullah Masood, one of the most active Taliban commanders in the north-west region of Pakistan, vowed to send suicide bombers to kill her.
Another Taliban commander, Haji Omar, told Reuters: "She has an agreement with America. We will carry out attacks on Benazir Bhutto as we did on General Pervez Musharraf."
"Definitely, it is the work of the militants and terrorists," Javed Iqbal Cheema, an interior ministry spokesman said, adding that it was too early to say which group was involved.
Manzoor Mughal, a senior police official involved in the investigation, told Reuters that the first of last night's blasts had been caused by a hand grenade. "The second was the suicide attack," he said. "The attacker ran into the crowd and blew himself up."
The bombings happened shortly after midnight, more than 10 hours after Ms Bhutto had arrived from Dubai. She escaped unhurt and was evacuated to her residence in the city.
A procession that had attracted several hundred thousand of her supporters was abandoned in chaos. Eight hours' earlier, the opposition leader had flown into Karachi, ending eight years of self-imposed exile in Dubai and London.
Last night's attack is likely to deepen the ongoing political crisis against the backdrop of a surge in Islamist violence.
Local television stations captured the two blasts, which occurred in quick succession near a heavily-protected truck carrying Ms Bhutto and her party leaders.
Television footage showed onlookers running towards the vehicle after the first blast, only to be caught in the second explosion. Party official Qasim Zia said Ms Bhutto had descended into the vehicle to use the bathroom at the time of the explosion.
TV stations showed graphic images of mutilated bodies lying on a street littered with debris, body parts and lumps of charred flesh. A blazing police vehicle stood beside the deserted Bhutto truck, which was emblazoned with the slogan "Long Live Bhutto".
"People were shouting for help, but there was no one to help them out. It smelled like blood and smoke," the Associated Press photographer, B K Bangash, who was 50 metres from the explosion, said.
The government had mounted a huge security operation to protect Ms Bhutto, who was travelling to the tomb of Pakistan's founder, Muhammad Ali Jinnah, where she planned to give a speech.
Around 20,000 security personnel lined the route and sophisticated anti-bomb jamming devices were fitted to her vehicle. Mobile phone signals were blocked in the area and armed bodyguards accompanied the truck.
The rooftop had been fitted with a bullet-proof enclosure but she spent most of the day standing at the front, chatting to party officials and waving to wellwishers.
Many of the dead were thought to be police and party security officials who had formed a moving security cordon around the vehicle. A local television cameraman also died.
Ms Bhutto's information secretary, Sherry Rehman, and the Punjab parliamentarian Abida Hussain were seen being carried away by officials.
Government security officials met in Islamabad last night to discuss further measures to protect Ms Bhutto, who had planned to hold a rally in her home town, Larkana, this weekend.
The Taliban had threatened to kill her after she suggested that she would help US troops to hunt for Osama bin Laden and other al-Qaida fugitives inside Pakistan.
Intelligence reports suggested that at least three groups with al-Qaida or Taliban links were plotting suicide attacks, according to a provincial official quoted by Reuters.
Ms Bhutto returned from exile hoping to win a third term as prime minister at general elections due to be held by mid-January. With encouragement from the US, she has been holding power-sharing talks with Gen Musharraf.
Speaking from Dubai, her husband, Asif Ali Zardari, implied that members of the Pakistani security services, the ISI, were responsible. "I blame government for these blasts," he told Aryone World Television. "It is the work of the intelligence agencies."
Pakistan's deputy information minister, Tariq Azim Khan, said Ms Bhutto had disregarded warnings to delay her return.
"She was given friendly advice she should delay her return," he said. "Obviously, she did not take it."
Asked what extra measures the government could possibly have taken given the size of the crowd, he said: "There can never be 100% foolproof security, but you can provide extra efforts. We tried to make the maximum effort possible."
The attack will be seen as a wider assault on the political system in Pakistan. Violent extremists have gathered force in the country this year. In July, an eight-day siege of the extremist Red Mosque in Islamabad in July left more than 100 people dead.
After arriving home, Ms Bhutto said she would help the country to defeat extremism. "That's not the real image of Pakistan. The people that you see outside are the real image of Pakistan," she added.
"These are the decent and hardworking middle-classes and working classes of Pakistan who want to be empowered so they can build a moderate, modern nation."
Last night's violence could endanger her power-sharing talks with Gen Musharraf, who has threatened to impose emergency rule or martial law if his plans to retain power are frustrated.
© 2007 The Guardian