Russia has unexpectedly freed opposition leader Alexei Navalny on bail after thousands of people protested over his jailing.

Protesters denounced his five-year jail sentence as a crude attempt by President Vladimir Putin to silence him.

The United States and European Union had voiced concern over the conviction, saying it raised questions about the rule of law and Russia's treatment of Mr Putin's opponents.

A judge approved the unusual prosecution request to release him while he awaits the outcome of an appeal.

The anti-corruption campaigner's movements will be restricted to Moscow.

Navalny proclaimed the ruling, one day after he was convicted of theft, as a victory for people power.

"I am very grateful to all the people who supported us, all the people who went to (protest in Moscow's) Manezh Square and other squares," the 37-year-old said.

"We understand perfectly well what has happened now. It's an absolutely unique phenomenon in Russian justice," he said in the court in Kirov, an industrial city 900km northeast of Moscow.

People poured onto the streets of big Russian cities to protest yesterday evening after Navalny was convicted of stealing at least 16 million roubles (€376,000) from a timber firm when he was advising the Kirov regional governor in 2009.

Police said more than 200 people were detained in St Petersburg and Moscow although there were no big clashes.

Navalny says the case was politically motivated and intended to sideline him as a political threat to Mr Putin, even though his support is limited outside the big cities and opinion polls show the president is still Russia's most popular politician.

Navalny led anti-Putin protests, which attracted tens of thousands last year, before they started to fade when the former KGB spy was elected to a six-year third term as president.