Russia's foreign ministry announced counter-measures in response to tough new sanctions proposed by the United States, ordering Washington to reduce its diplomatic and technical staff in Moscow and other cities.
The protests are the second mass action since March 26 called by Alexei Navalny, who has announced his intention to run for president next year and has drawn a new generation to the streets through a relentless online campaign.
US National Security Advisor Michael Flynn discussed the issue of US sanctions with Russia's ambassador weeks before Donald Trump was sworn in as president. The talks took place just as then-President Barack Obama was ordering new actions against Russia over its alleged interference in the US election.
Top Russian opposition leader Alexei Navalny was found guilty on Wednesday of embezzlement and given a five-year suspended sentence that threatens to end his bid to challenge President Vladimir Putin in a presidential poll next year.