"The Home Ministry has sent instructions to the intelligence departments of different security forces, seeking detailed information about the network established by the Maoists in several parts of Northeast, especially Assam and Nagaland," a top defence official told PTI in Shillong.

The Centre's instruction comes in the wake of a revelation from an arrested senior Maoist cadre in Jharkhand that the rebel group has already formed units in different districts of Assam, including Karbi Anglong and Golaghat.

Defence sources confirmed that CPI-Maoist central committee member Mahru Mahto alias Narayan Mahto, who was arrested in November from Bokaro, had admitted that there were growing network of the Maoists in the Northeast, especially in Assam.

What is more worrying, according to the official, is the nexus between the Maoists and some rebel groups of the Northeast like All Adivashi National Liberation Army and the NSCN-IM.

"Inputs gathered so far suggest that the AANLA commander Nirmal Tirkey is operating from Jharkhand and Andhra Pradesh. A group of over 100 AANLA cadres are undergoing training somewhere in Jharkhand, while the NSCN-IM is supplying arms to the Adivasi rebels," the official said, while not ruling out the possibility of the presence of Maoists in the Northeast.

Formed in Assam's Golaghat district in 2003 to push the interest of the Adivasi or tea plantation workers' community across the state, AANLA shot into the limelight after the group claimed responsibility for the bomb attack on a Delhi-bound Rajdhani Express train in Assam that killed five passengers and injured nine others.

Police say the AANLA is trying to capitalise on the Adivasi sentiments after the community's agitation for scheduled tribe status gained momentum, following the November 24 rally in Guwahati, which turned violent after protesters clashed with local residents.

During the initial days after its formation, the ANLA received patronage from the Kuki Revolutionary Army, active in Karbi Anglong district. Later, the NSCN-IM took the group under its wings.

The police say that the affinity of AANLA rebels with the Maoists is not surprising, owing to the characteristic similarities between the rebel groups.