Russia opposition leader Alexei Navalny fined for libel Published duration 22 April 2014

image copyright AP image caption Alexei Navalny, who frequently blogs about corruption, is currently banned from using the internet

A Moscow court has imposed a big fine on Russian opposition leader Alexei Navalny for libelling a district councillor on Twitter.

Alexei Lisovenko sued him for calling him "a drug addict" in a tweet.

Navalny denies he could have sent the message and is appealing against the 300,000-rouble (£5,000; $8,400) fine.

Navalny is an anti-corruption crusader and one of the chief critics of President Vladimir Putin. He is already under house arrest, in a separate case.

Under the conditions of his house arrest, imposed two months ago, he is barred from receiving visitors or communicating on social media. His Twitter account is managed by assistants.

Largely ignored by Russia's main state-owned media, Navalny has relied heavily on social media to mobilise his supporters and organise rallies.

He is serving a five-year suspended sentence for the alleged theft of 16m roubles from a timber firm in 2009.

A court is expected to rule later this week on whether Navalny's house arrest will be extended or he will return to prison. His libel conviction could mean that his suspended sentence will be converted into jail time.

Last year Navalny came second in Moscow's mayoral election, supported by one third of voters. He has always insisted the accusations against him are politically motivated.