A group of 10 ANVC militants from Garo Hills in Meghalaya had come to Darangthop under Agia police station for collecting extortion money, district Superintendent of Police Shyamal Prasad Saikia told PTI.
A small boy noticed a pistol with one of the ultras of the proscribed outfit and raised an alarm, Saikia said.
The locals encircled two of the militants, beat them up and they died, he said.
Two other extremists were apprehended by the security forces, while six others fled away, he said.
The deceased were identified as Nabang Changma and Wasi Changma, while the apprehended ones are Rupak Marak and Ismat Marak.
The undergrounds were initially suspected to be cadres of the Garo National Liberation Army (GNLA) in Meghalaya, the SP said adding that their interrogation revealed they were from the ANVC.