The trouble in the east Indian city began when a protest march turned violent and there were several pitched battles. Hundreds of demonstrators threw rocks and bottles at riot police, who had been deployed to the narrow streets of downtown Kolkata and used teargas.

Police later said vehicles had been set on fire and scores of demonstrators and police officers had been injured. Schools and offices were shut down and the city came to a standstill.

In recent weeks, the east Indian city has witnessed dozens of protests against reported police brutality and the killing of villagers in the West Bengal village of Nandigram by suspected communist cadres.

Villagers have been protesting against the state government's plans to industrialise parts of West Bengal for months. Many fear that their land will be taken away and they will not get sufficient compensation. The last week has seen fierce clashes between government supporters and opponents.

Coinciding protests

The situation was exacerbated on Wednesday by a separate protest against the government of West Bengal giving refuge to Bangladeshi author Taslima Nasreen, who has been accused of criticising Islam in her books.

The leader of the All India Minority Forum Idris Ali could not understand why the protest had turned violent: "We have been trying to keep peace from the beginning but in some parts of the city there has been violence. I have heard there are some anti-social activities but we are not part of them, nor are we supporting them."

When the violence got out of hand, the central government decided to send in the army and a curfew was imposed on central Kolkata.

"The police couldn't tackle the situation because they are all goons, they were hurling stones. So the police had to use teargas shells and the RAF (Rapid Action Force) came in to help them. The situation spread like wildfire. In the evening, when everything had lost control, the government decided to impose military personnel and a curfew was declared," explained a senior advocate of the high court Pradip Kumar Guha.

Embarrassing to communists

It is the first time in years that the Indian army has been deployed to quell violence in a big city. It is a major embarrassment to the state's communist rulers, who many complain have not brought an end to the violence instigated by their cadres. West Bengal has the world's longest-serving democratically-elected communist government.

The violence in Kolkata also disrupted the national parliament in the capital New Delhi. Angry lawmakers shouted at their communist counterparts in the Upper House. The chaos forced the chamber to be adjourned for the day. Meanwhile, in the Lower House the trouble in Kolkata coincided with a debate on the violence in Nandigram.