KARACHI (AFP) - Former Pakistani premier Benazir Bhutto vowed Friday she would never surrender to militants, after a suicide bomber killed 138 people in an "attack on democracy" that wrecked her jubilant homecoming.
Bhutto was unhurt in Thursday night's attack, having climbed into her specially fortified vehicle just moments before two explosions ripped through crowds welcoming her back to Karachi after eight years in exile.
The streets of Pakistan's biggest city, packed with hundreds of thousands of her supporters, quickly became a scene of bloody carnage as the nuclear-armed nation plunged into fresh political turmoil.
"It was an attack on democracy and it was an attack on the very unity and integrity of Pakistan," Bhutto told a press conference in the port city, wearing a black armband in memory of the victims,
Bhutto pledged to defy "cowards" from Al-Qaeda, the Taliban and other militant groups who had vowed to launch suicide attacks against her before she flew home from Dubai.
"If it means sacrificing our lives, then we are prepared to risk our lives, but we are not prepared to surrender our great nation to the militants," said Bhutto.
She further promised to stay in Pakistan to fight general elections in January, seen as a key step to returning the Islamic republic of some 160 million people to civilian rule.
It was the worst suicide attack in Pakistan's history and cast a cloud over hopes that her return, under a deal cut with President Pervez Musharraf, might end months of unrest in the South Asian country.
Military ruler Musharraf called Bhutto to offer his condolences and pledged to arrest the culprits behind the "terrorist attack", his spokesman said.
Bhutto earlier accused Islamist supporters of late military ruler Mohammed Zia ul-Haq of being behind the blasts, in an interview published in French on the Internet site of Paris Match magazine.
Zia overthrew Bhutto's father, prime minister Zulfiqar Ali Bhutto, in 1977 and had him hanged two years later, while her brother was shot dead here in 1996.
The explosions -- a grenade followed by a suicide blast -- came hours after Bhutto had flown home, sobbing as she set foot on Pakistani soil for the first time since 1999 after shrugged off warnings of militant attacks.
"It was like walking through an abattoir," said an AFP photographer who was nearby when the bombing occurred. Hospital officials said nearly 400 people were injured.
The explosion damaged Bhutto's campaign bus decked out with portraits of the ex-prime minister and her father, on which she had been driven through the crushing crowds for more than eight hours.
Interior ministry spokesman Javed Cheema said a grenade was thrown into the crowd seconds before the suicide attacker struck. The explosives were packed with pellets and nails, he added.
He said the blast "appears to be the handiwork of militants who have been creating acts of terrorism in the country."
Karachi was in shock Friday with shops and schools closed, as families headed to morgues to retrieve bodies of those killed.
"He died while protecting our leader. At least she (Bhutto) survived," said Mashook Ali, whose 17-year-old son Raib was among supporters who acted as a self-styled security detachment working close to Bhutto's truck.
Deputy information minister Tariq Azeem said there had been a prior threat by Baitullah Mehsud, a pro-Taliban warlord linked to a string of attacks since July, to attack Bhutto.
A purported spokesman for Mehsud later denied involvement.
Bhutto's husband Asif Ali Zardari however blamed one of the country's three powerful intelligence agencies.
Bhutto had returned from self-imposed exile after Musharraf dropped corruption charges against her in the hope her popularity could shore up his grip on power.
She had mostly worked out a power-sharing deal with him, but his re-election as president earlier this month is now being challenged in the courts.
The United States, which sees Pakistan as a key ally in its "war on terror," led the global outcry to the blasts. The White House said Islamic extremists were likely to blame, and Washington offered help with the investigation.
Australia said the attack bore the hallmarks of Al-Qaeda, while UN Secretary General Ban Ki-moon denounced the bombing.