More than 4,000 activists have been detained across Russia in fresh demonstrations demanding the release of jailed Kremlin critic Alexei Navalny. 

Authorities have ramped up pressure on supporters of the opposition leader in recent weeks, issuing warnings against participating in unauthorized rallies and threatening criminal charges against protesters.

However, this didn't deter Navalny aides from calling for new nationwide protests ahead of his trial set to start on February 2.

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Demonstrations kicked off in Russia's Far East, with dozens of protesters gathering at Vladivstok's central square despite police shutting the area off. Those who couldn't get past the authorities instead took to the frozen waters of the Amur Bay and started to dance in a circle.

Russian authorities have issued several warnings against participating in the unauthorized rallies and threatened criminal charges against protesters. 

According to the independent OVD-Info monitor, 4,027 people were detained, including 1,167 people in the capital Moscow, where footage showed security services using tasers against some of the protesters. 

In Moscow, authorities took the almost unprecedented decision to close seven of the capital's metro stations, limiting pedestrians movement in the city center. Some centrally-located restaurants and shops were also closed, with overground transport diverted. 

The rejuvenation of the protests in support of Navalny follows the 44-year-old opposition leader arriving at a Moscow airport on January 17 from Germany, where he had been recovering from exposure to a nerve toxin.

He was quickly detained on arrival as he waits to face trial on charges of violating the terms of a 2014 suspended sentence. 

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The Moscow rally was set to be outside the headquarters of the Federal Security Service, Russia's main security agency, which Navalny has accused of carrying out the near-fatal poisoning attack. 

Sunday's demonstrations come one week after tens of thousands of protesters gathered in over 100 cities across Russia to protest against the government. 

More than 4,000 were detained while the authorities launched several criminal probes against activists, also pressuring online platforms like Facebook and TikTok to delete posts with calls for rallies.

The country's media watchdog has since summoned representatives of the social media networks for failing to comply.

In the last week, Navalny's brother Oleg and his lawyer Lyubov Sobol were placed under house arrest for breaking coronavirus rules by calling for protests. On Saturday his spokeswoman Kira Yarmysh was detained for the same reason on the day she was set to finish a nine-day jail term for violating protest laws. 

Navalny is facing charges of fraud in a criminal case, according to the head of his Anti-Corruption Foundation, Ivan Zhdanov, linked to a probe launched last year into the opposition leader allegedly misappropriating more than $4 million of donations to his organizations. 

New sanctions?

The protests come as European Union foreign policy chief Josep Borrell heads to Moscow on Thursday amid calls for new sanctions against Russia in light of the government's treatment of Navalny.

While Borrell will also be looking for Moscow's help in resuscitating the 2015 nuclear pact with Iran, the opposition leader's fate is expected to be central to Borrell's conversation with his Russian counterpart Sergei Lavrov on Thursday. 

But the three-day trip to Russia – the first for a top Brussels envoy since 2017 – has caused controversy among the bloc's 27 members, with some seeing the visit as sending the wrong signal to the Kremlin.

However, the former Spanish minister has stated he would pass on a "clear message" to the Russian government. 

"The relationship with Russia is one of the EU's most complex. Recent developments only serve to further underline the need for me to visit Moscow," Borrell said in a statement Friday. 

"But beyond the issues of contention there are also areas in which the EU and Russia do cooperate, or need to cooperate more, that require our urgent attention."

Some EU members, including Lithuania, Latvia, Estonia, Italy and Romania, have called for new sanctions over the crackdown but so far the EU has yet to act as it awaits the conclusion of Navalny's trial. 

Relations between the two powers have been strained since 2014 following the Crimea crisis and Moscow's alleged role in the Ukraine conflict. 

At the time, the EU put in place economic sanctions against Russia, including a ban on buying or selling certain products from state-owned Russian banks, as well as an embargo on arms imports and exports between Russia and the bloc. Those sanctions run out on January 31. 

In October, the bloc also slapped asset freezes and visa bans on six senior Russian officials over the "use of chemical weapons in the assassination attempt" of Navalny.

As for the new sanctions, German Foreign Minister Heiko Maas said last week: "We have agreed today to wait for the court's decision, to wait to see... whether Alexei Navalny is set free after 30 days." 

However, the EU – in particular its central powers France and Germany – will first have to weigh the potential consequences of new sanctions taking a toll on Russian oil and gas exports to the bloc.

As Maas said: "This is not over."