“Preliminary investigations have revealed that Debnath was carrying the bomb to plant somewhere else,” West Bengal police inspector general Anuj Sharma said, adding the blast could be felt two kilometres away.

“A timer device had been fitted to trigger the explosion, but the bomb went off suddenly while he was on the bridge.

“Debnath was blown in half ... We do not think it was a suicide attack,” Sharma added.

Police had received a tip-off about a possible attack and arrested three suspected KLO followers before the explosion, which was carried two days before the anniversary of the group’s founding in 1996, said Sharma.

Ten people were also injured when the bomb exploded late on Thursday. Earlier reports put the number of dead at four but a fifth victim died later in hospital.

The KLO has carried out several other bombings with devices strapped to bicycles and has also marked its anniversary with attacks in the past.

Sharma said the KLO were behind a 2009 bombing in Jalpaiguri that killed four and an attack at a train station in November 2006 that claimed seven lives.

The KLO wants to create a separate state of Kamtapur in northern West Bengal that would include the tea-growing region of Darjeeling and five other districts, some of which border Bangladesh and Bhutan. It would also incorporate parts of the neighbouring state of Assam.

West Bengal is one of India’s largest states and Jalpaiguri is some 600 kilometres north of the state capital Calcutta.

The Indian government agreed in July to the creation of the new state of Telangana by splitting Andhra Pradesh, a move that critics said would fuel separatist campaigns.

India has been wracked by separatist conflicts since its independence in 1947, most notably in Kashmir and the remote northeast region.