New Delhi, India (CNN) -- A six-year-old boy was killed and 18 others were injured as a bomb explosion derailed a train in India's restive northeastern region Thursday, authorities said.
At least six cars and the locomotive of the train jumped the track because of the blast that occurred at early Thursday morning in Assam state, said S. Hajong, spokesman for India's northeast frontier railway.
He told CNN that the explosive device was believed to have been planted on the railroad.
The stricken train was heading to Kolkata in the state of West Bengal from Guwahati in Assam.
Police suspect the attack in the state's Kokrajhar district was carried out by a faction of the National Democratic Front of Bodoland (NDFB).
One group of the rebel outfit is holding talks with the Indian government. It signed a ceasefire agreement with federal and state authorities in 2005.
But counter-insurgency operations by security forces continue against militants opposed to dialogue.
"The anti-talks faction of the NDFB is the suspect (in Thursday's explosion)," Kokrajhar district police chief Prasanta Dutta told CNN.
He insisted police had intercepted radio messages about rebel plans to target rail and road transport.
The NDFB was formed in 1986 to fight for a separate state for the ethnic Bodo communities, officials say.