The toll in the Jalpaiguri bicycle bomb blast rose to six on Saturday with one of the critically injured persons succumbing to injuries.
The victim, a resident of the Bajrapara where the blast took place on Thursday, died at North Bengal Medical College Hospital in the early hours, hospital superintendent Amarendranath Sarkar said.
Meanwhile, an alert has been sounded across the district in view of the foundation day of Kamtapur Liberation Organisation, the ultra outfit against whom the needle of suspicion is pointed.
Police said patrolling has been intensified in the border areas of the district, which is adjacent to Bangladesh, Bhutan and Nepal.
Security has been stepped up at Alipurduar, which forms part of the inter-state border with Assam and has been the hub of KLO activities in the past.
Combat forces of the police and sniffer dogs have been deployed, while additional reinforcements have been rushed to the vulnerable areas, the police said.
The abandoned bag found near a level crossing in Jalpaiguri town, which created panic in the area on Friday, was opened by the police bomb squad and found to contain a few papers.
The KLO, an organisation formed in 1993 to fight for a separate Kamtapuri state comprising six districts of north Bengal and some areas of lower Assam, had denied involvement in the blast.