- Navalny's lawyers intend to appeal against his arrest later on Thursday.
MOSCOW: Several allies of jailed Kremlin critic Alexei Navalny were taken into custody early on Thursday after police raided their apartments and offices ahead of planned demonstrations.
The searches were connected to a criminal probe launched by the interior ministry over alleged violations of coronavirus restrictions during protests last week, Navalny's aides said.
The opposition has called for fresh demonstrations on Sunday to demand freedom for Navalny, who was arrested on his return from Germany where he had been covering from a poisoning attack.
Navalny's lawyers intend to appeal against his arrest later on Thursday.
Ivan Zhdanov, the head of Navalny's FBK Anti-Corruption Foundation, said prominent aide Lyubov Sobol and Navalny's brother Oleg were detained for 48 hours as suspects.
Sobol's lawyer Vladimir Voronin said both she and Oleg Navalny were questioned by police during the night.
Searches were also carried out at the flat of Navalny's wife Yulia, and in the office of FBK, Navalny's organisation, which is known for its investigations into the wealth of Russia's elites.
Police also arrived at the home of Navalny's doctor Anastasia Vasilyeva, who was also detained for 48 hours.
In a video posted on Twitter by Vasilyeva's press secretary, the doctor is playing Beethoven on the piano as people in uniform arrive at the door.
According to Mediazona, a news website that focuses on opposition detentions, police carried out at least 18 searches on Wednesday.
Tens of thousands of Russians across the country rallied last weekend in support of Navalny, who is awaiting a trial that could see him imprisoned for several years on charges of violating a 2014 suspended sentence.
Officials have also threatened to fine social media including Instagram, Twitter and TikTok for failing to delete posts urging young people to join illegal rallies.
Protests in Russia are banned if they are not approved by the authorities, as are calls for people under 18 to join in.
President Vladimir Putin's spokesman Dmitry Peskov told reporters on Thursday that the state did not want social networks to become "platforms to announce illegal protests".
The Investigative Committee, which probes major crimes, said it had launched a probe against Leonid Volkov, the head of Navalny's regional network, for persuading young people to protest.
The opposition plans to hold more rallies on Sunday, which in Moscow will take place outside the headquarters of the FSB, the security agency that Navalny says targeted him in the near-fatal poisoning attack.
More than 3,900 people were detained last Saturday at the unsanctioned rallies, which have sparked a series of criminal investigations.
The Moscow prosecutor's office said it had sent out warnings ahead of Sunday's rally to six individuals and five internet platforms without naming them.
Despite pressure from authorities and threats of arrest, the opposition appears unwilling to back down.
Political analyst Alexander Baunov of the Carnegie Moscow Center told AFP that Navalny "is ready to pay the price to become a real counterweight to Putin".
"What Navalny wants to do now is to prepare for a situation when he, as the main opposition leader, can become a real contender for power."