Maoists have a presence in almost 200 Indian districts
India's Prime Minister Manmohan Singh says his country is losing the battle against Maoist rebels.
Mr Singh told a meeting of police chiefs from different states that rebel violence was increasing and the Maoists' appeal was growing.
The rebels say they are fighting for the rights of the poor.
They operate in a large swathe of territory across central India, and in some areas have almost replaced the local government.
More than 6,000 people have been killed during their 20-year fight for a communist state.
"I have consistently held that in many ways, left-wing extremism poses perhaps the gravest internal security threat our country faces," Mr Singh told a conference of Indian police chiefs in the capital, Delhi.
"We have discussed this in the last five years and I would like to state frankly that we have not achieved as much success as we would have liked in containing this menace."
The prime minister said that despite the government's best efforts, violence in Maoist-affected areas was going up.
The prime minister admitted that the Maoists had growing appeal among a large section of Indian society, including tribal communities, the rural poor as well as sections of the intelligentsia and the youth.
Mr Singh said a more sensitive approach was necessary in dealing with the Maoists.
"Dealing with left-wing extremism requires a nuanced strategy - a holistic approach. It cannot be treated simply as a law and order problem."
The rebels operate in 182 districts in India, mainly in the states of Jharkhand, Bihar, Andhra Pradesh, Chhattisgarh, Madhya Pradesh, Maharashtra and West Bengal.
In some areas they have virtually replaced the local government and are able to mount spectacular attacks on government installations.