New Delhi - Indian government troops moved Thursday to end a siege by Maoist rebels who took control of a region in the eastern state of West Bengal by going on a rampage against the ruling communists.

"The operation at Lalgarh [area] started this morning. The operation will be mainly done by the state police but we will be adequately assisted by federal forces," West Bengal police chief Sujit Kumar Sarkar told the PTI news agency.

Sarkar declined to give the timeframe of the campaign to flush out Maoist guerrillas who have been organizing a tribal movement with a group called the People's Committee Against Police Atrocities.

The state police will be assisted by 500 members of the federal Central Reserve Police Force, including 200 officers from the Cobra unit, trained in anti-Maoist operations, he said.

But the rebels, supported by hundreds of villagers, were determined to put up a tough fight in Lalgarh, situated in West Midnapore district about 170 kilometers south-west of state capital Kolkata.

They used trees to block roads to prevent security forces from advancing, and there were also reports that the rebels were digging up roads to lay landmines.

The government was moving ahead slowly to minimize civilian casualties and urged tribal people not to collaborate with the Maoists, said Nilotpal Basu, a leader from Bengal's Communist Party of India-Marxist (CPI-M), the senior partner in the state's ruling coalition of left-wing parties.

"The government wants to ensure that the bloodshed is minimal ... you must understand that the Maoists are coercing people - yesterday Maoist leaders said they would use women and children as human shields," Basu said.

Lalgarh town and its neighbouring cluster of villages have been out of bounds for government officials and police since November 2008.

The tribal people in the area were organized by Maoists to form a local militia after some villagers were arrested in connection with a landmine blast, aimed at West Bengal Chief Minister Buddhadev Bhattacharya as his convoy passed through the area.

Bhattacharya escaped narrowly, but locals allege that young men in the area were tortured and harassed after the incident.

The Maoists, who have claimed responsibility for the mine, say they are helping to organize and focus the anger of local people.

Since Sunday, thousands of tribesmen backed by armed Maoist rebels have torched police stations, CPI-M offices and shot dead seven party workers in and around Lalgarh in a violent takeover of what has been a communist bastion for over three decades.

The Maoists claimed it as their first "liberated" zone in West Bengal. Maoist guerrillas, who operate in 13 Indian states, say they are fighting for the rights of the landless, poor and tribal people.

According to unofficial estimates, more than 3,000 people, including rebels, have been killed in Maoist violence since January 2005. (dpa)