MOSCOW, Feb 2: Over 5,100 people have been arrested in a countrywide crackdown on protesters rallying for the release of detained Opposition leader Alexei Navalny, who had recently been poisoned with Novichok nerve agent by Russian Intelligence agents while in Serbia and was treated in Germany.

Russia is known to be the only country that has been manufacturing and using chemical nerve agents like Novichok to silence rebels inside and enemies abroad over several decades. There have been plenty of reports of its spies poisoning its opponents in other countries like the UK too.

The massive protests held throughout the country last weekend and continued through Sunday were some of the largest seen in recent times in Russia. The anti-Putin rallies are rattling Kremlin.

His supporters have called for another protest in Moscow for Tuesday, when he is scheduled to face a court trial that could send him to prison, likely triggering violent confrontation with the police.

When Navalny, 44, was poisoned last August and collapsed on a flight in Siberia, he was flown to Germany for emergency medical treatment by his supporters . He was returning to Russia on January 17 as he recovered, despite warnings by well-wishers. He was whisked away by the police from a Moscow airport on arrival. As he left he kissed his wife Yulia, who, alongwith a group of journalists, had flown with him from Germany.

Thousands had gathered at a Moscow airport to greet his flight from Berlin, but the plane was diverted. Navalny was taken away by police at Sheremetyevo airport where the plane landed.

The then US President-elect Joe Biden's incoming national security adviser Jake Sullivan had said, "The Kremlin's attacks on Mr Navalny are not just a violation of human rights, but an affront to the Russian people who want their voices heard."

A month ago, investigative reporters named three agents of Russia's FSB security service who had travelled to Tomsk at the time Navalny was there, and said the specialist unit had tailed him for years, BBC reported.