Forensic experts and police on Tuesday sifted through the debris of a train compartment ripped apart by a blast in north Bengal that killed seven persons amidst suspicions that the attack was the handiwork of the Kamtapur Liberation Organisation or the United Liberation Front of Asom.

A central team has been sent to Belakoba station, where the blast occurred on the Haldibari-Siliguri passenger train on Monday, to ascertain which extremist group was behind the blast, Chief Minister Buddhadeb Bhattacharya said in a statement in the assembly.

Forensic specialists and a police team were trying to ascertain the explosives used in the blast that left 50 injured, of whom 20 are in a critical condition.

With the death of one person at the North Bengal Medical College and Hospital on Tuesday, the toll rose to seven, police said.

The chief minister, who spoke to Union Home Minister Shivraj Patil, said seven persons were killed in the blast and the toll could rise further.

Inspector General (Railways) Tushar Bhattacharjee had put the toll at eight on Monday night.

Police and intelligence officials believe the attack was carried out by the banned ULFA as the site of the blast is not far from the border with Assam.

The finger of suspicion has also been pointed at the KLO, an insurgent group propped up by the ULFA that is active in north Bengal.

Bhattacharya announced compensation of Rs 50,000 for the next of kin of those killed and said the state will bear the medical expenses of the injured.

Intelligence officials in Siliguri said the Darjeeling Mail, to which two bogies of the Haldibari-Siliguri train were to be attached, could have been the target.

The Mail, coming from Coochbehar district bordering Assam, was 30 minutes behind schedule when the blast occured.

The casualties would have been higher if the explosion had occurred at New Jalpaiguri Railway station near Siliguri, they said.

The officials said it was likely that the explosives went off at Belakoba while being carried to New Jalpaiguri.

The chief minister said state Ministers Partha De and Subhas Chakraborty would visit Belakoba on Wednesday.

Another minister Jogesh Burman is already there. The Northeastern Frontier Railway announced an immediate grant of Rs 15,000 for families of those killed, Rs 5,000 for the seriously injured and Rs 500 for those with minor injuries.

Chief Secretary Amit Kiran Deb refused to admit that the explosion was the result of an intelligence failure.

Inspector General of Police (Law and Order) Raj Kanojia said following the blast, a special alert had been sounded across the state, particularly at railway stations and bus terminals.

He added a special investigation team had been formed to ascertain who was behind the attack.