Indiahave a presence in 182 districts of
Maoist rebels in India and a leading separatist group in the country's north-east have decided to work together, according to a statement.
The rebels and the Revolutionary Peoples Front (RPF) of Manipur said they would fight to "overthrow" India's ruling regime.
The RPF is one of Manipur's oldest separatist groups.
It has an armed wing which attacks Indian security forces and punishes drug peddlers and woman traffickers.
Formed in 1976, a number of RPF's early leaders were trained in China.
A joint statement signed by S Gunen, the RPF secretary-general, and Comrade Alok of the underground Maoist party said they supported the "great Indian class struggle led by the Maoists against India's semi-feudal, semi-colonial regime".
has said the Maoist insurgency is the "single biggest threat" to India's security.
They operate in 182 districts in India, mainly in the states of Jharkhand, Bihar, Madhya Pradesh, Maharashtra and ., ,
The rebels say they are fighting for the rights of poor peasants and landless workers.