At least one policeman was seriously injured on Saturday when suspected Ulfa militants hurled a grenade during an encounter at Bordumgsa in Assam's Tinsukia district.
The police said during patrolling a group of Ulfa militants encountered the security forces and an exchange of firing took place.
During the encounter the militants lobbed a grenade in which one policeman was injured and he was admitted to Assam Medical College Hospital at Dibrugarh, the police said.
The militants escaped immediately after the incident.
Meanwhile, six cadre of United Peoples Democratic Front, which has been active in Arunachal Pradesh and Tripura, were arrested today from Arunachal's Changlang district bordering Tinsukia.
They are being interrogated in Tinsukia police station.