Assam Police Inspector General (BTAD) L R Bishnoi said the encounter took place in the early hours on the west side of Hel river at Dimruguri under Basugaon police station.
The four have been identified as Mohor, Domsatorong, Loharun and Maisaran, he said.
Bishnoi said the team also recovered one AK-56 rifle, one AK-56 magazine, 20 live rounds of ammunition, three pistols and five mobile sets.