Seven insurgent outfits of the north-east, including outlawed All Tripura Tiger Force (ATTF) and National Liberation Front of Tripura, have given a call for observing Independence Day as 'Black Day'.
All police stations in Tripura were put on maximum alert and BSF was alerted so that no insurgent could cross the 856 km-long Indo-Bangla international border in Tripura from their hideout in Bangladesh.
Patrolling by CRPF and Tripura State Rifles (TSR) was intensified in remote tribal and insurgency-prone areas and security was heightened in vital installations like the civil secretariat and Rajbhavan.
Police said all vehicles were being checked and bomb and dog squads were deployed in different parts of the state.
Sources in NF Railway said all Tripura-bound night services were either cancelled or rescheduled in view of the threats by the ultras.
Police said the Agartala airport was also put under high alert in view of the insurgents call and security was tightened.