The deceased were the members of United Peoples Democratic Front (Prasit).
In a statement, Inter Services Public Relations Directorate (ISPR), confirmed the incident on Monday.
The deceased were identified as Bhujendra Chakma, 45, Ruchil Chakma, 25 and Nabin Jyoti Chakma, 32.
Locals said, acting on a tip off, a team of army conducted a drive at Baradam area in the upazila. Sensing presence of them, 7 to 8 terrorists fired on them. In reply, army men also fired back. Later, bodies of three terrorists, two pistols and 8-round ammunition were recovered from the spot.
Uttam Chandra Deb, officer-in-charge of Dighinala Police Station, said the bodies were taken to the police station from the spot.