A Russian court has given opposition activist Alexei Navalny a suspended jail sentence after he was convicted in a high-profile fraud case.

Navalny was handed a suspended prison sentence of three-and-a-half years for defrauding two companies. His brother Oleg was handed a three-and-a-half year prison term for embezzlement.

Navalny has consistently denied the charges, which he said were fabricated on political grounds.

The Navalny brothers were convicted of defrauding two firms of 30m rubles (£335,159, $521,083) and were fined 500,000 rubles each.

The Kremlin critic has been an outspoken opponent of the Russian President Vladimir Putin and played a key role in the mass protests that swept through some Russian cities in 2011.

Navalny described the house-arrest sentence as the meanest possible sentence in a post on social media.

"Of all the possible sentences, this is the meanest," he wrote in Russian on Twitter.

Tuesday's sentencing was the latest episode in a series of criminal cases brought against the critic, who the Kremlin deems a dangerous challenge to its leadership.

Navalny ran for mayor in the Russian capital of Moscow in 2013, finishing in second place with 27% of the vote.

Following the sentencing, Navalny called on his supporters to hold street demonstrations.

"I call on everyone to take to the streets today," he said.

A rally has been organised to in Moscow's Manezh Square for 1900 local time (1600 GMT.)