Police said, "Initially, two bombs exploded, followed by 350 to 400 rounds of fire."
The National Investigation Agency and Nagaland Police have arrested three suspected activists of NDFB-S, including Ajoi Basamutary on whose alleged instructions 36 people were killed in Assam's Sonitpur area last month.
The Assam government had received prior intelligence report of an attack by terrorists of National Democratic Front of Bodoland-Songbijit but it did not know about the target and spots, said a senior official on Saturday.