The Kremlin's archenemy Alexei Navalny will remain in jail, a Russian court ruled Thursday, rejecting an appeal over his arrest ahead of anti-government protests this weekend.

Appearing in court by video link from jail, Navalny denounced the Kremlin's criminal proceedings against him as part of the government's efforts to intimidate the opposition.

"You won't succeed in scaring tens of millions of people who have been robbed by that government," he said, according to remarks carried by The Associated Press (AP). "Yes, you have the power now to put me in handcuffs, but it's not going to last forever."

Several of his allies were detained following police raids on their apartments and offices hours before the verdict and in the run-up to Sunday's rally outside Russia's Federal Security Service's (FSB) headquarters.

"This is blatant lawlessness to intimidate me and other people," Navalny told the court.

Police detained President Vladimir Putin’s critic at a Moscow airport after he returned to Russia on Jan. 17 from Germany, where he had been recovering from a near-fatal poisoning by a nerve toxin. The dissident was arrested and jailed for 30 days at the request of Russia's penitentiary service, which charged that he violated the probation terms of his suspended sentence from a 2014 money-laundering conviction that Navalny rejected as politically driven. He is also currently facing accusations in two separate criminal probes.

Police on Wednesday carried out searches at Navalny's flat in Moscow and at the homes of his allies over alleged violations of coronavirus restrictions during anti-Kremlin protests last week. 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 in a probe launched by the interior ministry. Searches were also carried out at the flat of Navalny's wife Yulia and at the office of the FBK, 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 detained for 48 hours too. In a video posted on Twitter by Vasilyeva's press secretary, the doctor was playing Beethoven on a piano as people in uniform arrived at the door.

Putin's spokesperson Dmitry Peskov said the searches and detentions are a legitimate part of police efforts to investigate the alleged violations during the events. "Law enforcement agencies are doing their job," Peskov said during a conference call with reporters. "There were numerous violations of Russian laws, and law enforcement agencies are at work."

Moscow police on Thursday issued a notice to the public not to join protests Sunday, warning that officers would act resolutely to disperse unsanctioned rallies and bring participants to justice.

Also Thursday, Russian prosecutors issued warnings to Facebook, Google, Twitter, TikTok and Russian social networks, demanding that they block calls for more protests. "The state doesn't want the social networks to become a platform for promoting such illegal actions," Peskov said.

Asked if a refusal to remove such content could prompt Russian authorities to block the platforms, Peskov said it would be up to relevant government agencies to consider a response. "All pros and cons will be weighed and, if necessary, measures envisaged by the law will be taken," he said.

Earlier this week, Russian state communications watchdog Roskomnadzor said it would fine Facebook, Instagram, Twitter, TikTok, YouTube and two Russian social networks for their failure to block calls on minors to join Saturday's protests. Facebook, Google and TikTok haven't responded to requests for comment about the Russian authorities' action.

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.

Russian police detained nearly 4,000 people last Saturday at the unsanctioned rallies, which have sparked a series of criminal investigations. Rights group Amnesty International on Thursday said Russian authorities "appear shamelessly bent on violating human rights by silencing their critics" and called their actions a "cowardly attempt" to prevent further protests in Navalny's support.

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. Volkov said on Telegram that Sunday's rallies will take place "despite searches and late-night interrogations, despite the 4,000 arrests last week, despite the lies and intimidation of Kremlin propaganda."

Political analyst Alexander Baunov of the Carnegie Moscow Center told Agence France-Presse (AFP) that Navalny's continued protest of the government was evidence that he was "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," he said.