As a judge prepares to give his verdict in the fraud trial of Russian protest leader Alexei Navalny, a growing number of President Vladimir Putin's opponents are facing trial and the prospect of long prison terms.

The court in the northern Kirov region on Thursday will rule whether the charismatic anti-corruption campaigner is guilty of embezzlement in a timber deal. Prosecutors have asked for a six-year prison sentence.

Navalny insists the allegations against him were "sewn with white threads" or blatantly cooked-up, dictated by the Kremlin.

But his trial is far from the only case in Russia to be condemned by activists as a throwback to Soviet-era repression, when political opponents were thrown into jail on arbitrary pretexts.

Criminal probes and in some cases trials are already under way for figures accused of rioting in the anti-Kremlin protests that rocked Putin ahead of his return to the presidency for a third term in May 2012.

These come on top of the widely publicised sentences dished out to anti-Kremlin tycoon Mikhail Khodorkovsky; and to the radical art collective Pussy Riot.

Opposition campaigners insist these were ordered from on high.

"The aim of the trials is to show who is boss... to scare the active part of society and make clear that opposition activity is a waste of time," pro-opposition political analyst Dmitry Oreshkin told AFP.

In early July, the opposition-backing mayor of Yaroslavl 300 kilometres northeast of Moscow was arrested along with several of his deputies, accused of extorting $420,000 from a businessman.

The mayor, Yevgeny Urlashov, is a former member of the ruling party United Russia who has gone over to the opposition. He has rejected the allegations, blaming pressure ahead of local elections where he planned to stand as a candidate.

"I was warned that they were going to get rid of me, it did not matter how," he told TV Rain channel. The businessman who denounced him was a member of the ruling party, he said.

Another opposition leader, Sergei Udaltsov, risks 10 years in a prison camp for "preparing to organise mass disorder".

He has also been charged with "taking part in mass riots" as part of clashes that followed a demonstration on May 6, 2012, in Moscow, on the eve of Putin's inauguration to a third Kremlin term.

Udaltsov has been confined to house arrest since February and banned from using the Internet or the phone. He categorically denies the charges against him.

Around 30 people have so far been charged over riots at the May 6 protest, of whom 12 went on trial last month in Moscow. They face the prospect of up to eight years in jail.

They are accused of throwing plastic bottles, overturning public toilet cubicles and resisting the police.

The opposition movement has accused police of deliberately provoking the clashes. It accuses the Kremlin of moving to crush the rights movement that grew up after the disputed legislative election of November 2011, which was won by Putin's United Russia party.

"The justice system in our country has been fulfilling political orders for a long time... But this process is growing in scale," said Lyudmila Alexeyeva, veteran rights activist and former Soviet dissident.

"Our state is undemocratic, authoritarian, and after the latest elections the authorities have consistently, hurriedly and even hysterically been building up a police state."

Some have decided to leave Russia for fear of arrest.

Former world chess champion turned anti-Kremlin activist Garry Kasparov announced in June from Geneva that he would not return to Russia.

If he returned to Moscow, he said, he had serious doubts about being able to leave again.

Kasparov was accused of biting a policeman on the hand at a protest in 2012, although a court acquitted him.

Another influential figure to flee Russia is top economist Sergei Guriyev.

He announced in June that he would stay in France for fear of being arrested after publicly supporting Navalny and criticising the second fraud conviction against Khodorkovsky in 2010.

The United States and the European Union have raised their voices in recent months.

They have condemned the Kremlin for harsh measures against the opposition and the adoption of laws limiting freedom of expression and the activities of NGOs.

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