In a statement issued to the media last night, the outfit said its activists triggered the explosion.
The blast had claimed the life of the security personnel and caused injuries to three others, the police officer said.
The AR personnel were on foot patrol at a site located at Ragailong Khuman Lampak Stadium road.
The three injured were identified as Himansu Devnath (31) of West Bengal, K Rameshwor (32) of Manipur and Manish Kumar (28) of Bihar.