A suspected suicide bomber killed 133 people in an attack on former Pakistani prime minister Benazir Bhutto, as she was driven through Karachi to greet supporters on her return from eight years in exile.

Bhutto was unhurt in one of the deadliest attacks in her country's history. She was quickly escorted away from the truck that had been carrying her from the airport through streets crowded with hundreds of thousands of well-wishers.

"Ms Bhutto is safe and she has been taken to her residence," said Karachi police chief Azhar Farooqui after two explosions in quick succession rocked Bhutto's motorcade.

There was no claim of responsibility. Militants linked to Al Qaeda, angered by Bhutto's support for the war on terrorism, had this week threatened to assassinate her.

Interior Ministry Secretary Syed Kamal Shah said 133 people had been killed and 290 wounded.

"The initial investigations suggest it was a suicide bombing," he said.

Bhutto was travelling in a platform-mounted truck. Police in vehicles escorting her, reporters and her supporters were among the casualties.

"The target was the truck," Farooqui said.

Reuters photographer Athar Hussain was slightly hurt. Hussain, on a truck behind Bhutto's vehicle, said "a ball of fire" burst into the air. He then rushed towards the scene.

"There was another blast and it was more powerful, then I knew it was a bomb attack."

He saw a television cameraman killed in front of him: "Bodies were scattered all over and wounded were crying for help."

Rehman Malik, a Bhutto aide with her on the truck, said the blasts went off while she was resting inside the vehicle.

The attack took place shortly after midnight, more than 10 hours after Bhutto had arrived from Dubai. A city-centre rally she was due to address was cancelled.

About 20,000 security personnel had been deployed to protect Bhutto but the provincial governor said in view of the "real threats", authorities had urged her party to wind up the  procession faster.

"Unfortunately, the terrorists got their opportunity," governor Ishrat-ul-Ibad told Dawn Television.

Dressed in a green tunic, her head covered with a white scarf -- green and white are Pakistan's national colours -- Bhutto had for hours stood in the open on top of the truck, ignoring police advice to stay behind bullet proof glass, as it edged through crowds waving party flags.

Bhutto appeared to have had forebodings of an attempt on her life.

"They might try to assassinate me. I have prepared my family and my loved ones for any possibility," she told the Asharq Al Awsat newspaper.

President Pervez Musharraf said in a statement the attack was "a conspiracy against democracy".

The US and other allies condemned the attack.Reuters