By Subir Bhaumik
BBC News, Calcutta
A bomb has ripped through a parcel van of a passenger train in India's north-east state of Assam, killing five people and injuring several others.
Passengers heard an explosion on the train Pic: Subhamoy Bhattacharjee
The Delhi-bound train had left Dibrugarh and was headed for the state capital Guwahati when it was hit by the explosion at around 0120 (1950 GMT).
A tribal guerrilla group, the Adivasi National Liberation Army, says it carried out the attack.
It wants the same rights for Adivasis that they have in other Indian states.
The Adivasis are descendants of tribals from central India who were taken to Assam during British rule to work in the tea gardens.
Adivasis in the states of Jharkhand and Bihar are classified as Scheduled Tribes, which gives them considerable benefits in education and employment.
"Our guerrillas used a remote controlled device to set off the explosion," Dilip Beg, a spokesman of the Adivasi National Liberation Army told the BBC.
"We shall continue with such attacks in the coming days, until the Assam government and the Indian government confers Scheduled Tribe status on the Adivasis."
Assam police intelligence chief Khagen Sarmah said there was a deep crater at the site of the explosion.
"It appears the explosive was planted on the track but we need more investigation to establish that," the official added.
The damaged train - the Rajdhani Express - was taken to Chongajan railway station and the passengers then taken to Guwahati on a separate train to enable them make the onward journey to Delhi.
On Monday, a Delhi-bound passenger train, the Brahmaputra Mail, was derailed near the railway junction of New Jalpaiguri in the neighbouring state of West Bengal, resulting in one death and several people injured.
Sabotage was not ruled out as the train was carrying a large number of Indian army soldiers and paramilitary troops going home to north Indian states on leave from Assam.
Assam has a number of insurgent groups, many of them are active in the area where Thursday's explosion took place.
These groups have a history of attacking the railways as they provide an easy target.