India stepped up security on its rail network and along its border with Bangladesh on Tuesday after a powerful blast on a train in West Bengal killed seven people and wounded at least 70.
The blast hit two crowded coaches late on Monday near a remote railway station in an insurgent-hit area of West Bengal, about 665 km north of Kolkata.
Police said anti-India rebels belonging to the United Liberation Front of Asom (ULFA) of Assam, and a local insurgent group, the Kamtapur Liberation Organisation (KLO), could have been behind the blast.
"The KLO had been dominant in the area for years and has become active again," Tapas Kumar Das, a senior police officer involved in the investigation, said.
Railway officials said hundreds of policemen were being deployed at railway stations and in trains across the country and more security checks and frisking would be conducted.
The KLO, formed in 1995, is demanding a separate Kamtapur state and is suspected to have links with ULFA rebels who have been fighting for Assam's independence for nearly three decades.
Officials say KLO rebels, as well as ULFA members, use neighbouring Bangladesh as a safe haven.
Border Security Force said an alert was sounded along the long and porous Bangladesh frontier after the blast and patrols had been stepped up.