Russian state prosecutors have demanded a six-year jail sentence for protest leader Alexei Navalny, one of President Vladimir Putin's biggest critics, on charges of theft.

Although prosecutor Sergei Bogdanov did not seek the maximum ten-year term possible at the trial in Kirov, a six-year sentence would keep Mr Navalny in prison until after the next presidential election in 2018.

Mr Navalny denies charges of stealing 16 million roubles (€370,000) from a local timber firm that he was advising in 2009 while working for the liberal regional governor.

He said the charges are intended to sideline him as a potential rival to Mr Putin.

"I ask the court to find Alexei Navalny guilty ... and sentence him to six years in prison and a fine of 1 million roubles," Mr Bogdanov told the court in Kirov, 550km northeast of Moscow.

Mr Navalny, 37, exchanged nervous smiles with his wife Yulia.

She then embraced him when a short break in proceedings was declared, and Mr Navalny told reporters: "I still hope everything will be fine."

The anti-corruption blogger, who helped organise the biggest anti-Putin protests since the former KGB spy first rose to power in 2000, is the most prominent opposition leader to be tried in post-Soviet Russia.

He has suggested Mr Putin ordered the trial to stop his criticism of "swindlers and thieves" in power.