The violence marred what had otherwise been a peaceful rally in St Petersburg, Russia's second city, attended by up to 3,000 anti-Putin activists.

It followed a similar event in Moscow on Saturday that ended in mass arrests and the temporary detention of the former world chess champion and arch Putin critic Garry Kasparov.

After his release, Mr Kasparov said Mr Putin's Russia was now somewhere between Belarus and Zimbabwe when it came to civil liberties and warned that the Kremlin had taken the gloves off.

"It is no longer a country ... where the government [even] tries to pretend it is playing by the letter and spirit of the law." Both anti-Kremlin demonstrations were organised by the Another Russia movement, a coalition of political forces that accuses Mr Putin of taking the world's largest country in an authoritarian direction.

Another Russia is demanding that parliamentary elections due to be held later this year be free and fair and that Mr Putin step down in favour of a more liberal figure.

He is due to hand over the reins of power next March after presidential elections are held, but the opposition fears that he will be replaced with a "Putin clone".

The event in St Petersburg turned violent when the crowd began to disperse and make their way to a nearby metro station.

It was at that point, according to protesters, that the police launched an unprovoked attack, beating people about the legs and the body with batons.

Up to 150 protesters were arrested in the violence that followed and bundled into police vans, where eyewitnesses claimed the beating continued.

Those arrested included Eduard Limonov, the leader of the radical National Bolshevik Party, and dozens of the event's organisers and speakers.

Marina Litvinovich, an aide to Mr Kasparov attending the rally, said that the violence used against protesters was unjustified and disproportionate.

"The meeting was peaceful and was finished when trouble started. The police simply started beating people. One man, a 65-year-old, had his leg broken."

A female official from the liberal Yabloko party, Olga Tsepilova, had her nose broken and sustained serious head injuries.

The police told a different version of events; they claimed that members of several radical youth movements had tried to break through police lines and pelted riot police with bottles and stones.

Although the rally was sanctioned by the authorities, protesters were warned beforehand that they should under no circumstances attempt to march down Nevsky Prospekt, the city's main street.

The police claimed that was exactly what the young radicals had tried to do and argued that they had been compelled to use force.

More broadly, the Kremlin accuses Another Russia of trying to destabilise the country and of orchestrating provocations designed to spark violence and generate headlines.