While no one immediately claimed responsibility for the attack, an intelligence official said an ethnic insurgent group, Karbi Longri National Liberation Front, fighting for wide autonomy in the state for the past five years was suspected.
The front is one of the three groups active in the region; the other two groups have reached ceasefire accords with the government.
The blast comes just days after terrorists attacked targets across Mumbai, killing more than 180 people. Today's blast, however, is not seen as related to the Mumbai attacks.
In October, the state had witnessed 13 coordinated bomb attacks which killed 77 people and wounded hundreds in four towns.