Acting on a tip-off, a joint team of police and army personnel launched an operation in Nabang village under Krishnai police station of the district along the Assam- Meghalaya border, they said.
A group of militants opened fire on the security forces and an encounter followed in which an ultra was killed while the others managed to escape.
The security forces recovered a US carbine from the slain militant, sources said, adding that combing operations were on to nab the others who escaped.