Former Prime Minister Benezir Bhutto, her return from exile shattered by a homicide attack that killed up to 136 people, blamed militants Friday for trying to kill her and said she would not "surrender our great nation" to them.

Bhutto said there were two attackers in the deadly bombing, and that her security guards found a third man armed with a pistol and another with a suicide vest. Ahead of her arrival, she said, she was warned suicide squads were dispatched to kill her.

"There was one suicide squad from the Taliban elements, one suicide squad from al-Qaida, one suicide squad from Pakistani Taliban and a fourth -- a group -- I believe from Karachi," she said.

Baitullah Mehsud, a top militant leader on the unstable Afghan border, threatened this month to meet Bhutto's return to Pakistan with suicide attacks, according to local media reports. An associate of Mehsud, however, denied Taliban involvement.

Bhutto said her guards prevented more carnage.

"They stood their ground, and they stood all around the truck, and they refused to let the suicide bomber -- the second suicide bomber -- get near the truck," she said.

Bhutto blamed militants for the attack, which drew international condemnation.

"We believe democracy alone can save Pakistan from disintegration and a militant takeover," she told a news conference. "We are prepared to risk our lives and we are prepared to risk our liberty, but we are not prepared to surrender our great nation to the militants."

Bhutto's procession crept toward the center of Karachi for 10 hours with supporters thronging her armored truck when a small explosion erupted near the front of the vehicle. That was quickly followed by a larger blast, destroying two police vans escorting the procession. Interior Minister Aftab Khan Sherpao said the vehicles on the left side of Bhutto's truck suffered the brunt of the blast, one of the deadliest in Pakistan's history.

Bhutto did not blame the government, but said it was suspicious that streetlights failed after sunset Thursday when her convoy was inching its way through the streets of Karachi. She said attempts to reach the national security adviser to have the lights restored were unsuccessful -- phone lines were also apparently down.

"I'm not accusing the government but certain individuals who abuse their positions and powers," she said. "We were scanning the crowd with the floodlights, but it was difficult to scan the crowds because there was so much darkness."

The top security official in the province where the attack took place suggested that Bhutto's camp had not seriously considered the need for security for her return after eight years in exile.

"They got carried away by political exigencies instead of taking our concern seriously," said the official, Ghulam Muhammad Mohtarem.

There was no immediate claim of responsibility for the attack, which drew international condemnation.

Manzur Mughal, the Karachi police officer in charge of the investigation, said detectives had established that a young man who threw a grenade blew himself up 22 seconds later next to the truck.

The attacker's head was found nearby and taken to a forensic lab to try to identify him, Mughal told The Associated Press.

Bhutto survived unscathed, but the explosions that went off near the bulletproof truck she was riding in turned her jubilant homecoming parade into a scene of carnage, ripping victims apart and hurling a fireball into the sky. The attack shattered the windows of her truck. She appeared dazed afterward and was escorted to her Karachi home.

Police on Friday collected forensic evidence including pieces of flesh and shoes from the site of the bombing. Bhutto's armored truck, which carried signs that read "Long Live Bhutto," was hoisted away using a crane. One side bearing a big portrait of the former premier was spattered with blood and riddled with shrapnel holes.

President Gen. Pervez Musharraf phoned Bhutto Friday to express his shock and profound grief over the bombing and prayed for the former premier's safety and security, his spokesman said.

"The president expressed his strong resolve that a thorough investigation would be carried out in order to bring the perpetrators of this heinous crime to justice," spokesman Rashid Qureshi said.

Musharraf said earlier that he was "deeply shocked" by the attack and condemned it in the strongest possible terms as part of a "conspiracy against democracy," the state-run Associated Press of Pakistan said.

Mohtarem said nuts, bolts and steel balls packed around the explosives had made the bombing so deadly. He said it was impossible to prevent more such attacks.

Mehsud's spokesman could not be reached for comment, but an alleged associate of the militant commander, Isa Khan, denied Taliban involvement.

"The government's secret agencies are involved in it. Taliban have no part in it," Khan told an AP reporter by phone from the volatile northwestern tribal town of Bannu, where he is believed to command pro-Taliban militants loyal to Mehsud.

"This was an effort to provoke common people and create hatred against the Taliban. We do not do anything that harm common people," he said.

Bhutto has made enemies of Islamic militants by taking a pro-American line and negotiating a possible moderate, U.S.-friendly alliance with Musharraf, a longtime political rival despite their shared liberal values. The attack cast a pall over Bhutto's talks with Musharraf and possible plans for such an alliance.

It remained unclear whether the attack would stiffen the two leaders' resolve to fight militancy together or strain already bad relations between Bhutto and the ruling party.

Musharraf won re-election to the presidency in a vote this month by lawmakers that is being challenged in the Supreme Court. If he is confirmed for a new five-year presidential term, Musharraf has promised to quit the military and restore civilian rule.

Bhutto plans to contest parliamentary elections due in January, and has ambitions to win a third term as prime minister.

Railways Minister Sheikh Rashid Ahmed said that he has asked the government to make the election campaign short after consultation with political parties, amid concern that large gatherings could be vulnerable to attacks. Police put Thursday's crowd at 150,000.

Officials at six hospitals in Karachi reported 136 dead and around 250 wounded.

Karachi police chief Azhar Farooqi said that 113 people died, including 20 policemen, and that 300 people were wounded. It was not immediately possible to reconcile the differing death tolls.

Qureshi, the presidential spokesman, said he doubted the attack would deflect Bhutto from her course.

"If someone thinks that by spreading this kind of terror they will stop the political process in Pakistan, I don't think that's correct, I don't think that will happen," Qureshi told the AP.

In Karachi, which lies in the far south of Pakistan and has been buffeted by militant attacks, schools were closed on Friday and traffic was thin.

Bhutto paved her route back to Pakistan through negotiations with Musharraf that yielded an amnesty covering the corruption charges that made Bhutto leave Pakistan.

Bhutto had brushed off militant threats, dismissing authorities' appeals for her to use a helicopter to travel into Karachi to reduce the risk.

"I am not scared. I am thinking of my mission," she had told reporters on the plane from Dubai.

Leaving the airport, Bhutto refused to use a bulletproof glass cubicle that had been built atop the truck taking her toward the tomb of Pakistan's founding father, Mohammed Ali Jinnah.

The former premier had just gone to a downstairs compartment in the truck for a rest when the blast occurred, said Christina Lamb, Bhutto's biographer.

"So she wasn't on top in the open like rest of us, so that just saved her," Lamb told Sky News.

The United States, the United Nations, the European Union, China, Afghanistan and India were among those who condemned the attack.

"Extremists will not be allowed to stop Pakistanis from selecting their representatives through an open and democratic process," said Gordon Johndroe, foreign affairs spokesman for President Bush.