An express train has been derailed after a bomb exploded on the track in a remote north-eastern Indian state.

The engine and unoccupied carriages of the Kamrup Express went off the tracks after the explosion near Diphu station in Assam state.

The tracks were damaged, but there are no reports of injuries.

The train was on its way from Calcutta to the Assam state capital, Guwahati, and was carrying around 700 passengers.

A senior police official said the passengers had been lucky because ''the militants failed to trigger the remote controlled blast properly''.

The engine, an empty compartment, a parcel van and a brake van were derailed, a railway spokesperson said.

Rebels

Senior police officials said separatist rebels could have carried out the attack.

"We presume it is an attempt to create panic ahead of India's Republic Day on 26 January," Assam Police Chief Hare Krishna Deka said.

Separatist groups in India's north-east routinely call for a boycott of Republic Day celebrations, which usually feature grand parades and an exhibition of military hardware.

In the past, the rebels have also targeted vital oil installations and transport links.

Assam is the gateway to the north-east and is linked to the rest of India by a tiny strip of land.

Several groups of insurgents are active in north-east India, many fighting for territorial rights.