More than 120 people were feared dead last night and scores more were injured after suspected suicide bombers targeted a convoy carrying former Pakistan prime minister Benazir Bhutto following her return from eight years in exile.

Ms Bhutto was being driven from Karachi airport to a rally to mark her homecoming when the two blasts occurred. The streets were crowded with about 200,000 wellwishers who had turned out to greet her.

Officials said she was unhurt after one of the deadliest attacks in Pakistan's history. "Ms Bhutto is safe and she has been taken to her residence," Azhar Farooqui, a senior police officer in Karachi, said.

The attack followed threats issued earlier this week to assassinate her by several Islamist groups, including pro-Taliban militants linked to al Qaeda angered by her support for the United States' global war on terrorism.

The blasts occurred despite a huge security presence.

Police cordoned off the scene of the blasts. The area around a stage where she was scheduled to deliver a speech to supporters was evacuated.

Doctor Ejaz Ahmed, a police surgeon, said 80 dead were taken to three hospitals. A journalist counted 35 bodies at another hospital.

An interior ministry spokesman said 240 people were wounded.

Rescuers scrambled to drag bodies from the twisted wreckage of blazing vehicles as flames lit up the night sky after two apparent explosions in Pakistan's most violent city.

"The blasts hit two police vehicles which were escorting the bus carrying Ms Bhutto. The target was the bus," Mr Farooqui said. At least eight police officers were feared among the dead.

Rehman Malik, one of Ms Bhutto's aides, who was travelling with her on the bus, said the blasts went off while she was resting inside the vehicle.

The attack brought swift condemnation.

Pakistan President Pervez Musharraf, in a statement issued by the state-run news agency, said it was "a conspiracy against democracy".

In Washington, Gordon Johndroe, White House National Security Council spokesman said: "The United States condemns the violent attack in Pakistan and mourns the loss of innocent life there.

"Extremists will not be allowed to stop Pakistanis from selecting their representatives through an open and democratic process."

Foreign Secretary David Miliband condemned the Karachi bomb blasts, saying: "I condemn utterly the use of violence against entirely innocent people and the attempt to suppress the right of Pakistanis to express their democratic voice. I share the shock of the Pakistani community in the United Kingdom at these horrific attacks."

Speaking from Dubai, Ms Bhutto's husband, Asif Ali Zardari, said: "I blame the government for these blasts. It is the work of the intelligence agencies."

The first blast was apparently relatively minor but was followed by a much larger blast close to the front of a bus carrying Ms Bhutto, which broke its windows and door.

Faranza Raja, a spokeswoman for the Pakistan People's Party (PPP), said: "There was blood all around and it was chaos... we couldn't understand what was happening all around. We didn't know where to go, what to do."

Most of the dead were believed to be members of the PPP. A cameraman with a local radio station was also killed.

Local journalists said Ms Bhutto may have survived through being shielded from the blast by an overhang because she was sitting on top of the bus at the time.

She had flown in from Dubai earlier in the day accompanied on the flight by about 100 PPP members.

Intelligence reports suggested at least three jihadi groups linked to al Qaeda and the Taliban were plotting suicide attacks, according to a provincial official.

Some 20,000 security personnel had been deployed to provide protection on Ms Bhutto's return.

She had returned from self-imposed exile to lead the PPP into national elections intended to return the country to civilian rule.

Ms Bhutto had vowed to return to Pakistan for years to help end the military dictatorship and was seen as a potential ally for President Musharraf, the army chief who took power in a 1999 coup.