The ambush on the joint patrolling party of the CRPF and Assam police took place about an hour before a 48-hour bandh by KPLT began in the district and in Dima Hasao Hills at 5 pm as part of its call for boycott of the Republic Day celebrations, police said.
The incident took place at Koilamati on the banks of Bogijan river in Bokajan sub division when a joint patrol team comprising about 15 CRPF and police personnel were fired upon by the suspected militants from nearby forests.
CRPF jawan, Yambal Darlam of the 149 Battalion, died on the spot, while Assam police Havaldar Debakanta Laskar was seriously injured in the ambush, the police said.
The security forces returned the fire and the militants fled from the area.
An operation has been launched to track down the militants, the police added.