United Liberation Front of Asom militants struck for the second time within 12-hours since Wednesday night exploding a bomb in a bus killing one person and injuring 37 others in Assam's Kokrajhar district this morning, official sources said.

Official reports reaching Guwahati said the bus, which was on its way to Cooch Behar in North Bengal from Sapotgram in Dhubri, had stopped at the Gossaigaon weekly market when the helper saw an unclaimed object and shouted 'bomb'.

The police, which was nearby, rushed to the spot but before they could defuse the bomb it went off killing 16-year-old Ranjit Singh and injuring 37 others, mostly bus passengers who were having breakfast in a nearby roadside hotel.

The police, who had earlier said it was the work of NDFB militants, now confirmed that it was the handiwork of ULFA militants, as the NDFB, which was otherwise active in Kokrajhar district, has neglible presence in the area.

The casualties could have been more, as the bus was overcrowded but most of the passengers had alighted from the vehicle for breakfast.

The injured were admitted to Kokrajhar civil hospital where condition of some of them was stated to be serious, the sources said.

Last night ULFA militants threw a hand grenade killing one person and injuring eight others in front of a cinema hall in Dibrugarh township.

Meanwhile, according to police another blast took place last night in Kokrajhar district on the railway track between Fakiragram and Chautara railway station of the North East Frontier railway just after a goods train had crossed.

Police confirmed it was a blast and did not rule out the possibility of militants targetting trains crossing the area at that time.

The track suffered cracks as a result of the blast and traffic had to be halted for nearly five hours, police said.

Traffic was restored early this morning after the railway track was repaired.

Security has been intensified in the entire district in view of the blasts with additional forces deployed near vital installations and railway track to prevent sabotage.