Security forces have been carrying out operations to flush out Maoist extremists from the Lalgarh region in West Bengal since last month. The rebels had been backing tribals there who had virtually converted the whole area into a free zone.

Banerjee said: 'Atrocities were being committed in Lalgarh in the name of Maoists...We want justice, we want the political murderers to be arrested.'

The railway minister asserted that as many as 50 Trinamool Congress workers had been killed in two months in West Bengal.

The CPI-M, however, alleged that the Trinamool was providing shelter to Maoists and fomenting extremist violence, thus posing a 'grave threat to the entire nation'.

Its senior politburo member Sitaram Yechury alleged that the Maoists were 'operating under the banner of the organisations set up by the Trinamool Congress.'

He said: 'By giving shelter to Maoists, the Trinamool Congress is posing a grave threat to the entire nation.'

'Why is the Trinamool hesitating to demarcate themselves from the Maoists? They are still using the Maoists for political purposes. This will continue till the 2011 (assembly) elections (in the state).'