The Maoists are being squeezed in their traditional central heartland
India's Maoists have spread north-east, gaining a foothold in the strategically located states bordering China and Burma, officials and analysts say.
The Maoists are filling the void created by dwindling ethnic insurgent groups like the Ulfa, an Institute for Conflict Management (ICM) report says.
One key Assam official told the BBC that boys thought to have gone south for jobs had instead joined the rebels.
The Maoists have become squeezed in their traditional central states.
'Extortion letters'
The ICM, an Indian security think-tank, said the Communist Party of India (Maoist) (CPI-M) had made determined moves to replace the dwindling Ulfa, NSCN and PLA insurgent groups.
Deaths related to violence by these groups have been in steep decline and the organisations are being progressively marginalised.
India's Maoist Insurgency
- Violent rebellion began in 1967 in West Bengal village of Naxalbari and spread over rural areas of central and eastern India
- Led by elusive military commander Kishenji, supported by between 10,000 and 20,000 fighters
- More than 6,000 killed since rebellion began
- Bloodiest attacks on security forces include 76 killed in April 2010 ambush; 55 killed in 2007 attack on police post
Ajit Singh, author of the report, said the Maoists had come under tremendous pressure in their core areas of central and northern India.
They are short of arms and ammunition to fight the large number of security personnel ranged against them. The north-east provides a way to procure Chinese weapons.
Iftiqar Hussein, who administers five sensitive districts of Upper Assam, told the BBC officials had become aware of the Maoist build-up after arresting and interrogating young boys.
"The Maoist guerrillas are getting food and shelter in the area. There were several cases of arms-snatching. Even extortion letters were sent to some rich people," he said.
Intelligence officers say that many of the large number of young boys thought to be leaving to find jobs in southern states had in fact left their villages to join the Maoists.
Mr Hussein agreed, saying: "We have found out such a situation prevailing in an area called Sadia near the Arunachal Pradesh border."
Retired police officer, Subir Dutta, a specialist in Maoist and north-eastern affairs, told the BBC the Maoists had been trying to gain a foothold in the north-east for 20 years and appear to have now succeeded.
Maoist representation there, initially with the Maoist Communist Centre, which merged with the CPI in 2004 to form the CPI-M, had been dominated by ethnic insurgency movements.
But most of these have became marginalised or have begun negotiations with the government.
Ajit Singh said the Maoists had adopted the strategy of supporting mass movements, such as opposition to dams or support for the creation of new administrative districts.
The issues are local in nature but enjoy huge popular support.
Police say they have made a number of arrests of suspected Maoists involved in such movements.
Leaders of such campaigns in Assam insist they have no links to Maoists and say the government is trying crush their movements with the claims