Indian security forces have intensified their operations against Maoist rebels, officials say.
Thousands of forces have joined those already operating in jungle areas of three eastern states where the rebels have a formidable presence.
A major security offensive – Operation Green Hunt – to flush out the rebels is under way in several states.
More than 6,000 people have died during the rebels’ 20-year fight for communist rule in many Indian states.
The rebels have a presence in about a third of India’s 600-odd districts.
Prime Minister Manmohan Singh has described the Maoist insurgency as India’s “greatest internal security challenge”.
The newly-arrived federal forces are now moving into the jungles of West Bengal, Orissa and Jharkhand states that may house a number of rebel hideouts.
West Bengal police chief Bhupinder Singh said 6,000 new forces had arrived in the state’s Purulia and West Midnapore districts, which have seen rebel violence.
In neighbouring Jharkhand state, police chief Neyaz Ahmed said that federal forces along with local armed police had begun attacking rebels hideouts in the jungles.
“We have seized a lot of explosives and destroyed a few rebel camps,” he said.
With the chance of peaceful negotiations with the government fading, the Maoist military wing chief Koteswara Rao has threatened to attack targets in cities across Bengal and Orissa.
But Mr Rao said his offer of a 72-day ceasefire with government forces still stands. He has also named three “intellectuals” to mediate between the government and the rebels.
The government has not reacted to the latest demand of the rebels, and called some of their demands “bizarre”.