Guwahati, Jul 13 (IANS): Assam Police Wednesday arrested two tribal separatists belonging to a ragtag rebel army for the weekend train explosion that left nearly 100 people injured, an officer said.

A police spokesperson said the two arrested rebels belonged to the Adivasi People's Army (APA).

"We are interrogating the two APA militants and trying to get details of their modus operandi," a senior police officer said, requesting not to be named as he is not authorized to speak on record.

A powerful bomb planted on the track ripped apart the Guwahati-Puri Express late Sunday near Ghograpara in western Assam's Nalbari distict, about 70 km from Assam's main city of Guwahati.

Four coaches of the train derailed, trapping scores of passengers, leaving 103 passengers injured.

"We are getting vital leads but cannot divulge details at this stage. We should be able to pick up some more APA rebels who were involved in the bombing," the police officer interrogating the two arrested rebels said.

The APA is a rebel group fighting for more autonomy for the tea plantation community in Assam and also seeking scheduled tribe status for the nearly 500,000 tea tribespeople in Assam.

"We believe the APA has an estimated strength of just about 50 to 60 militants, of which there could be some 15 to 20 armed cadres," the officer said.

Police earlier suspected the outlawed National Democratic Front of Bodoland (NDFB) of masterminding the explosion.

"From our reports we can say that the NDFB was probably not involved in the attack. We have got some serious clues as to who carried out the blast, but cannot divulge anything now as it could jeopardize the investigations," Assam Chief Minister Tarun Gogoi said.