Guwahati: The "joint military command" of Myanmar-based NSCN (Khaplang) and Paresh Barua-led Ulfa (Independent) on Monday claimed responsibility for Sunday's ambush in Nagaland's Mon district that killed two soldiers and critically injured four.

The joint statement said a joint team of Assam Rifles and 164 Territorial Army (Naga) battalion was attacked as part of their "joint military operation" near Tenyak river, about 2km from Aboi town in Mon district. It, however, claimed that "four soldiers were killed and six or more injured and guns and weapons recovered".

It said the attack was carried out "to enhance the progress of the national liberation movement of Western Southeast Asia."

The Myanmar-based NSCN (K) considers the entire Northeast and parts of Myanmar as "Western Southeast Asia" which it wants to liberate from India and Myanmar. Ulfa (I), led by Paresh Barua, wants sovereignty for Assam and is against joining talks without discussion on its core demand.

Soon after NSCN (K) abrogated ceasefire with the Centre in 2015, the two outfits formed the "joint military command" and targeted the army in Manipur, Arunachal Pradesh and Assam, particularly along the border with Myanmar. Although the two outfits had assisted each other in the past, they decided to carry out joint attacks in 2015 following operations by security forces both in Nagaland and Assam.

An Assam Rifles spokesperson told The Telegraph on Monday that the deceased had been identified as Fatey Singh Negi (of Assam Rifles) from Uttarakhand and Hangnga Konyak (of 164 Territorial Army (Naga) battalion) from Nagaland. "The four injured (all from Assam Rifles) are being treated at Indian Air Force hospital in Jorhat in Upper Assam. Their condition is still critical," he said.

Security officials said army teams were being targeted as they deterred militant movement through unfenced stretch of the border to their camps in Myanmar.

"Although most of our army personnel deployed in the Northeast are well-trained in jungle warfare, they (the militants), being locals, have an upper hand as they are well-acquainted with the terrain," admitted an army officer.

The Northeast shares 1,642km of border with Myanmar in Arunachal Pradesh, Manipur, Nagaland and Mizoram.

Six Assam Rifles personnel were gunned down by a joint team of militants in Manipur's Chandel district in May 2016 which was followed by the killing of three army jawans in Upper Assam's Tinsukia district in November that year and two more in Lower Dibang Valley district in Arunachal Pradesh in April this year. All the three attacks were close to the Myanmar border or on the Assam-Arunachal Pradesh border which the outfits use as their transit route.

Ulfa extortion: The Ulfa (I) on Monday alleged that some "spies" of the army and Assam police were issuing extortion demands to tea gardens and business establishments in Dibrugarh and Tinsukia districts in Upper Assam in the outfit's name. In a statement issued by its publicity wing, it said it had not issued any extortion demands in the two districts and in Namsai, Lohit, Dibang and Changlang districts in neighbouring Arunachal Pradesh.