The marches on Monday organised by the BJP to the offices of the district magistrates across Bengal in protest of the August 9 rape and murder at RG Kar hospital turned violent in at least two north Bengal districts, prompting the police to burst teargas shells and use water cannons to disperse crowds.

In Cooch Behar and Alipurduar, violence sparked as the BJP supporters, while heading towards the DM’s office, broke barricades raised by the police and resorted to brick-batting as the law enforcers tried to resist them.

On Monday afternoon, around 1,000 BJP supporters assembled near Sagar Dighi, a waterbody in the heart of Cooch Behar town surrounded by state government offices including the DM’s office.

Around 2pm, the BJP supporters tried to breach a barricade, prompting the police to spray water from a water cannon. Nisith Pramanik, the former BJP MP and Union minister of state joined the protests.

Soon, Pramanik's security personnel had a skirmish with policemen. The police detained Pramanik, angering BJP supporters who started pelting bricks and stones at cops. The police retaliated by bursting tear gas shells.

The police also charged batons and nabbed some of the demonstrators who tried to break the barricade.

Pramanik was taken to the office of the superintendent of police while others were taken to the Kotwali police station. Later, the former MP was shifted to the district police lines.

Police stop the BJP supporters near the district magistrate's office in Cooch Behar on Monday

After an hour, the situation came under control. Some police personnel were injured, sources said.

In the evening, Pramanik was released.

District Trinamul leaders accused Pramanik of trying to foment tension in the town.

“On the pretext of a demonstration at the DM’s office. Nisith Pramanik and some goons backed by the BJP tried to create tension in the town. The police have shown restraint,” said Parthapratim Roy, TMC’s spokesperson in Cooch Behar, asking for appropriate steps against "all those who created tension".

The BJP leadership, in turn, accused the state police of resorting to highhandedness.

Biraj Bose, a district general secretary of BJP, said around 40 party supporters were injured, six seriously, in Monday's incident.

Sukanta Majumdar, the state BJP president, said: “The police acted strictly across the entire state (on Monday). However, in Cooch Behar, the police and the administration attacked and detained our leaders and workers without any provocation.”

In the neighbouring Alipurduar town, as the BJP supporters headed for the Dooars Kanya from the Balai Memorial Club ground, the police stopped them.

A section of the demonstrators turned violent and attacked the police with bricks, injuring around 12 police personnel. Around 200 cops were deployed in and around the collectorate to prevent the BJP supporters from advancing.

As BJP supporters broke a barricade, the police retaliated and used a water cannon and tear gas. Cops also chased the demonstrators with batons to clear the area.

“The agitators pelted stones at the police, which made us use the water cannon and tear gas. Twelve personnel from our side got injured and one of them is under treatment at the hospital,” said Y. Raghuvamshi, the Alipurduar superintendent of police.

Manoj Tigga, the BJP MP of Alipurduar who had joined the march, trained guns at the police. “The police resorted to coercion to stop our peaceful rally,” he said.

Such marches were also held in other parts of the state but no major incident was reported. In Suri of Birbhum, BJP supporters led by the party’s state general secretary Jagannath Chatterjee tried to breach a barricade. As they were stopped, Chatterjee, along with others, resorted to a sit-in demonstration at the spot for a while.