We've also not been able to arrest those top-rung Maoist leaders who have taken shelter in the inhospitable forest terrains of Lalgarh,' Sen said.

'As the central paramilitary forces would not stay in Lalgarh permanently, we'll have to plan for a time-bound operation, say for next 15-25 days, to improve the law and order situation in the region,' Sen said.

State's ruling Left Front (LF) chairman and Communist Party of India-Marxist (CPI-M) secretary Biman Bose expressed concern at the exodus from his party following heightened activities of the Maoists.

'The Maoists are adopting a hit-and-run policy and they will continue to do so,' he said. 'We are concerned about the exodus of our party cadres in the area due to the terror perpetrated by the Leftwing extremist group,' he said.

Lalgarh, about 200 km west of Kolkata, has been on the boil since November last year when a landmine exploded on the route of the convoy of Chief Minister Buddhadeb Bhattacharjee and two then central ministers-Ram Vilas Paswan and Jitin Prasada.

Alleging police atrocities after the blast, the Maoists, alongside the People's Committee Against Police Atrocities (PCAPA), launched an agitation and turned the area into a virtual 'free zone' by torching police camps and offices of the ruling communists and driving out the civil administration.

Maoists are active in areas under 21 police stations in the state's three western districts - West Midnapore, Bankura and Purulia.