The device, timed to explode at 1550 hours, was found in an abandoned ambassador car just opposite the offices of Chief Minister Prafulla Kumar Mahanta and his cabinet colleagues, official sources said.

The car is believed to have been left behind by militants earlier in the day.

Several ministers and bureaucrats were inside the secretariat when police cut open the petrol tank of the car to recover and defuse the bomb, the sources said.

It is still not known which extremist group had planted the bomb, but the hand of Bodo militants is suspected to be behind yesterday's blast which Mahanta had said might have been aimed at taking his life.

Police have sealed all the entry and exit points of the city,launched a massive search operation and picked up five persons for interrogation, the sources said.

The recovery of a driving licence from the spot of yesterday's blast indicated involvement of Bodo militants but the identity of the group involved was not immediately established, state DGP P V Sumant said.

Official sources said a local shopkeeper and a home guard of the Dispur police station spotted around 1000 hours an ambassador car parked at the spot for long.

Apprehending danger, the home guard immediately rang up the police station and policemen rushed to the spot.