A Russian court has sentenced opposition leader Alexei Navalny to five years in prison for embezzlement from a timber firm, sparking anger online.

Navalny, a prominent anti-corruption blogger, was jailed after he was found guilty of heading a group that embezzled 16 million rubles ($500,000) worth of timber from state-owned company Kirovles in 2009, The Associated Press reports.

“The court, having examined the case, has established that Navalny organized a crime and … the theft of property on a particularly large scale,” the judge said.

He denied the charges, saying the trial was politically motivated.

The verdict triggered a wave of outrage on social networking sites which he used effectively for his campaign against corruption in Russia.

Before he was handcuffed and led away, Navalny urged his supporters to continue his anti-corruption struggle.

“Don’t sit around doing nothing,” Navalny posted on his Twitter account.

Navalny called the dominant United Russia party “the party of crooks and thieves” and led anti-Putin protests in 2011. He also registered his candidacy for the next mayoral election in Moscow.

The EU said the verdict posed “serious questions” about the state of Russian law.

French foreign ministry spokesman Philippe Lalliot expressed concern.

“We note that not all judicial remedies have been exhausted and that the sentence could be reviewed on appeal,” Lalliot said.

Russian prosecutors demanded Navalny’s release pending appeal.