Explosives were found on the tracks where 13 coaches of a Maharashtra-bound express train derailed in West Midnapore district early Friday, strengthening suspicion of Maoist involvement in the incident.
"Gelatine sticks and TNT explosives were found on the tracks," South Eastern Railway General Manager AP Mishra told reporters in Jhargram.
Mishra said that the driver of the Gyaneswari Super Deluxe Express train heard a blast.
The assistant driver of the express was killed, he said.
Sniffer dogs have been taken to the site.
Railway Minister Mamata Banerjee, who is at the accident spot, told reporters that Maoists were observing 'black week' from Friday.
"Their anger is against the government, but they are making Railways their soft target," she said.
Asked if vigil was being maintained on railway tracks, Banerjee said, "There are 65,000 km of railway tracks in the country mostly through rural areas. How can we keep watch on such a vast stretch?"
She said extensive rescue operations were continuing with damaged bogies being cut open with gas cutters.
Sixty-five passengers were killed when the train derailed and five of its coaches were hit by a goods train coming from the opposite direction.
Police said that survivors were spotted in S2, S3 and S4 compartments which were tilting precariously on the goods train. They are being provided food and drinking water.
"We don't know the fate of the passengers of S5 and S6 compartments which have overturned," they said.