The blast occurred on the railway track last night about eight km south of Mazbat damaging a reinforced concrete cement (RCC) line sleeper, IGP L R Bishnoi said.
The explosion with a loud sound had occurred at around 9 PM but none reported it to police with the people thinking football fans had burst firecrackers to celebrate the Northeast United's win in the ISL football game, the police official said.
There is no information about the involvement of the NDFB(S) underground group in the blast, he added.
Another bomb was recovered on the same railway track this morning at Rowta in the district during investigations by police, Bishnoi said.
A bomb defusing squad along with CRPF Cobra team were searching the area for more bombs and railway technical staff were monitoring the track, he said.
Bishnoi said that more than 16 members, including the 'commander' of the UGPO have been arrested during the last 10 years.