The bridge, three kilometres from Sharif's private residence in Raiwind, was destroyed in the explosion. Sharif and his family were to have passed the bridge at that time on their way to Raiwind from Lahore. Their departure was delayed and they were at home in Lahore at the time of the blast. The family later flew from to Raiwind by helicopter.

Three civilians and a police officer died in the explosion, and three policemen have been wounded, doctors and police officers in Lahore said. Earlier, Assistant Superintendent of Police, Munir Sheikh, had said three policemen and one police officer died in the blast. ``We have sent special bomb disposal squad experts for investigations,'' he said.

Police blamed the ethnic Muttahida Qami Movement(MQM), a former ally of Sharif, for the explosion. A police official said three MQM workers had been arrested in the southern port city of Karachi on suspicion of planning the explosion. He did not disclose the identity of the suspects.

In Lahore, police raided the MQM office, but made no arrests. But an MQM leader, Sheikh Liaquat, Hussain said there was no question of his party's involvement in the incident.