Nine people were also injured in the attack at Bajrapara at around 7 pm, Police said.
"Five persons have died and nine were injured in a bomb blast at Bajrapara near the Jalpaiguri town. The explosives were kept on a bicycle. It went off on a culvert over a small river and a little distance away from St Pauls School," Shashikant Pujara, IG North Bengal, said.
Asked whether KLO or any terrorist organisation was behind the blast, Sharma evaded a direct reply saying, "We are investigating all the angles".
"As the KLO has been observing its martyrs' day today and December 28 is its foundation day, they are the suspects. We are yet to see whether it's an attack or a carrier was carrying explosives which went off accidentally," said Pujara.
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The nine injured had been admitted to the Jalpaiguri Sadar Hospital from where one was referred to the North Bengal Medical College Hospital.
The condition of some of the injured were critical, hospital sources said.
North Bengal Development Minister Gautam Deb said that the government would not tolerate this sort of activity and it would be dealt with sternly.
He said the state government would provide all facilities for the treatment of the injured.
Former CPI(M) minister and local leader Asok Bhattacharya alleged that the KLO recently regrouped and started subversive activities.