Four activists of Forward Bloc, a constituent of West Bengal's ruling Left Front, were killed on Tuesday and several injured when the police fired on party supporters during a law violation programme at Dinhata in Coochbehar district.

While the police put the death toll at four, FB claimed five activists were killed in the firing.

Twelve policemen were injured in brickbatting by FB activists in front of the sub-divisional officer's office at Dinhata, a traditional stronghold of the party.

Protesting the police action, the FB has called a 24-hour bandh in the state on Wednesday, which has been supported by the main opposition Trinamool Congress, the Congress and Left opposition Socialist Unity Centre of India.

The police said the firing was resorted to after teargas and lathicharge failed to quell FB workers who indulged in violence, arson and ransacked the SDO's office.

District Police Superintendent Anil Kumar told PTI that 12 policemen were injured in brickbatting by the mob, which also set on fire a police vehicle and vandalised government property.

All-India Forward Bloc general secretary Debabrata Biswas described the police firing as 'barbaric and unprovoked' and claimed the incident would have a 'definite impact' on the Left Front's unity.

"I would expect chief minister Buddhadev Bhattacharjee to take appropriate action against erring police officials and Left Front chairman Biman Bose to condemn the trigger-happy policemen who sought to suppress a democratic movement," Biswas said.

The incident would not only have its impact on Left unity in West Bengal, but all over the country, he said.

Main opposition Trinamool Congress chief Mamata Banerjee extended her party's support to the bandh and expressed her party's sympathy for those 'who fell victims to the bullets of the barbaric police of the Communist Party of India-Marxist-led Left Front".

"There is no rule of law in West Bengal where the ruling party has been consistently committing atrocities, not only on the opposition parties, but on the Left allies too," she alleged.

Banerjee alleged the CPI-M-led Left Front government was now leaving no one out of the 'Marxist wrath'. "We are not against Leftists, but against the CPI-M," she added.

Mamata said the bandh call has been supported by the Trinamool Congress and the party-led Progressive Democratic Secular Front 'in order to save democracy'.

"If necessary, TC workers would be on the streets to foil any attempt by the CPI-M to break the bandh," she said.

Mamata said the bandh call by a Front partner was 'unprecedented' in the history of the Left Front. She said the state government was not prepared to allow any democratic movement against its 'failures' but, "People's movement cannot be suppressed by the CPI-M-led government through brutal use of police force".

"The police have become trigger-happy under Left Front rule and resort to firing instead of trying to use other means to contain violence," she charged.