Russia's supreme court announced that it had liquidated the small Republican party, claiming that it had violated electoral law by having too few members. The party is one of very few left in Russia that criticises President Vladimir Putin.

The move against Russia's opposition came as pro-democracy activists prepared for the latest in a series of anti-government rallies that have infuriated Russia's hardline authorities.

Hundreds of demonstrators are expected to gather today in Nizhny Novgorod, Russia's fourth biggest city. The protesters from The Other Russia, a coalition of opposition groups, are expected to march despite attempts by pro-Kremlin officials to prevent them from demonstrating.

"The march's leaders are being called in by police and intimidated. We are half a step away from a police state," Denis Bilunov, a member of the march's organising committee, told the Guardian. "There isn't much point in talking about democracy in Russia any more."

Today's protest follows an opposition rally earlier this month in St Petersburg in which at least 5,000 people chanted slogans against Mr Putin, and which was violently dispersed by police.

The size of the last demonstration appears to have surprised the authorities. They have refused permission for the latest rally to go ahead and blocked the route.

On Thursday Moscow's prosecutor's office also suspended the Nationalist Bolshevik party, another radical and previously banned anti-Kremlin group. The National Bolshevik party is a radical activist group that has been a driving force behind recent anti-government protests, as the country prepares for parliamentary elections in December and next year's presidential vote.

Vladimir Ryzhkov, the leader of the Republican party, said yesterday that the ban was part of a Kremlin-inspired campaign to crack down on dissent. "This is part of the Kremlin's policy of suppressing the opposition. It's being done to prevent opposition parties from taking part in elections," he told the Guardian. "This is the fate any opposition party in Russia."

Mr Ryzhkov - one of a handful of independent MPs in the Duma, the lower chamber of parliament, and a leading Putin critic - said his party would appeal in Russia and to the European court of human rights.

Organisers of today's rally in Nizhny Novgorod say they have faced widespread intimidation by the city's pro-Kremlin authorities. Earlier this week police from the special organised crime unit of Russia's interior ministry seized 60,000 copies of an opposition newspaper due to be distributed during the demonstration.

The mayor's office announced a children's festival on the site of the proposed march, and blocked off the road to carry out what it said were urgent repairs.

"Taking to the streets isn't our plan," said Mr Bilunov. "But the problem is that the opposition is being pushed out of the legislative process. This is the only way we can protest legitimately. We are being barred from federal channels and from parliament."

The Other Russia brings together a series of diverse opposition groups hostile to the Kremlin. They include Gary Kasparov's United Civil Front, the Popular Democratic Union, led by Mikhail Kasaynov - a former prime minister who fell out with Mr Putin - and the National Bolsheviks.

Organisers also hope to attract the support of locals fed up with new construction in the city's historic heart, as well as environmentalists concerned about the destruction of green spaces.

At their last rally in St Petersburg the opposition marched under the slogan Those Who Don't Agree.

Yesterday the National Bolshevik leader, Eduard Limonov, predicted the latest ban on his party would lead to "big problems". He told Interfax news agency: "I am not afraid for my life. I am primarily afraid for my relatives and friends. I have accepted the prosecutor's office's challenge. We are launching a fight."

The Kremlin argues that its new electoral law - which says that all political parties must have 50,000 members and be represented in half of Russia's provinces - is meant to streamline Russia's untidy political scene. Critics say the legislation is designed to kill off smaller parties that oppose the Kremlin.

Backstory

Russia's tiny opposition is represented in the current Duma by four or five MPs. Pro-Kremlin parties predominate among the 447 deputies. The small opposition Republican party, banned yesterday, was formed by defectors from the Soviet Communist party. It emerged in 1990 on the wave of liberalism encouraged by then-Kremlin leader Mikhail Gorbachev. The Republican party has one MP, Vladimir Ryzhkov; its other attempts to win seats have repeatedly failed. But it has played a solid role in the liberal opposition. The liberal Yabloko party also has two MPs. Two other anti-Putin MPs sit as independents. In theory, the opposition includes Russia's Communist party and the far-right Liberal Democratic party. In reality, they rarely if ever voice opposition to the Kremlin, observers point out.