A massive security alert was sounded on Monday across Assam after the overnight separatist bombing that derailed a passenger train and left more than 100 people injured, 20 of them critically, officials said.
"We have sounded a high alert across the state with security personnel deployed at vulnerable locations to thwart rebel attacks," Chief Minister Tarun Gogoi said.
"We condemn such barbaric militant attacks like bombing trains or other such things targeting civilians," he added.
Police suspect militants of the outlawed National Democratic Front of Bodoland (NDFB) for the explosion at the Guwahati-Puri Express late on Sunday near Ghograpara in western Assam's Nalbari distict, about 70 km from the main city of Guwahati.
Four coaches of the train were derailed, trapping many passengers.
"It was indeed a very powerful explosion and the bomb was placed on the track. Flexible wires and other materials used to trigger the explosion were recovered from the accident site," a senior police officer said requesting anonymity.
"Forensic experts have collected material evidence from the site and only after examination we can be sure about the composition of the explosives," he said.
The train was bound for Puri in Bhubaneswar.
"There was a loud explosion and it was total chaos soon after. The coach in which I was travelling skidded of the track and fell in a marshy land with waist deep water. Somehow we managed to come out of the coach," said Jiten Das, a passenger who was among those injured.
"I sustained cut injuries on my head and arms, besides a wound in my chest."
"Four of the coaches derailed and one of the bogies skidded and went at least 20 metres from the track," Dhanmoni Das, a local who helped several of the injured come out of the train, said.
"We rescued more than 100 people and helped them reach the nearest hospitals with the help of bicycles, motorbikes and private vehicles," said Rubul Ali, another local who helped in the rescue operation.
The critically injured were shifted to the Gauhati Medical College and Hospital. No militant groups have claimed responsibility for the attack.
"We strongly suspect the NDFB to be behind the blast," the police officer said.
The NDFB is a group fighting for an independent homeland for the Bodo tribe's people in western and northern Assam. A faction of the NDFB is observing a ceasefire with New Delhi, while another faction headed by jailed chairman Ranjan Daimary is still waging a war for independence.
Meanwhile, all incoming and outgoing trains to Assam have been suspended following the blast.
"We are yet to retrieve the derailed bogies trapped in a marshy land a few metres away from the track. Until we repair the track, movement of trains would remain suspended," a railway official said.