MOSCOW — A judge ordered the Russian opposition leader Aleksei A. Navalny to be jailed for 30 days, ahead of a decision that could put him behind bars for years, after an extraordinary, rushed court hearing on Monday held inside a police station within a day of his return from Germany.
Moments after the judge announced her decision, Mr. Navalny called for protests in a video message to his supporters. One of his top aides, Leonid Volkov, said Mr. Navalny’s nationwide network was preparing to organize demonstrations across Russia on Saturday.
“Do not be afraid,” Mr. Navalny said in the video, which he had recorded in a makeshift courtroom set up in a police station meeting room. “Take to the streets. Don’t do it for me, do it for yourselves and for your future.”
The fast-paced events came the day after Mr. Navalny, who spent months abroad recovering from a near-deadly poisoning, was arrested at a Moscow airport on accusations of violating the terms of an earlier suspended prison sentence. He spent the night at a nearby police station without access to a lawyer.
President Vladimir V. Putin has long sought to minimize Mr. Navalny’s significance — down to not uttering his name — but the decision on how harshly to crack down on Mr. Navalny and his supporters in the coming weeks could have far-reaching implications for the Kremlin. On Monday, condemnation of Mr. Navalny’s arrest poured in from the United Nations and just about every major Western capital, but the Russian government breezily dismissed the criticism.
“We are not a lady coming out to a ball,” Foreign Minister Sergey V. Lavrov said during a news conference, responding to a question about the damage done to Russia’s international image.
As international pressure mounted, Mr. Navalny faced a judge not in a regular courtroom, but inside the police station in Khimki, a city bordering Moscow, where he was being held. A lawyer for Mr. Navalny, Vadim Kobzev, said he was notified of the hearing minutes before it started.
Several hours after the hearing began, Mr. Kobzev said that Mr. Navalny had been ordered jailed until Feb. 15, pending another hearing on charges of violating the terms of a three-and-a-half-year suspended prison sentence he received in 2014. Europe’s top human rights court said Mr. Navalny was unfairly convicted of financial crimes in that case.
Russia’s prison service claims that Mr. Navalny repeatedly violated parole, and it has petitioned to convert the suspended sentence into real jail time. If the court approves the petition, Mr. Navalny could remain in prison until July 2024 — after Russia’s next presidential election, which is scheduled to take place that March and in which Mr. Putin could run again.
Russia’s judicial system is not independent, but it usually aims to preserve the veneer of procedural impartiality in cases against opposition figures. On Monday, however, the authorities seemed to be doing all they could to keep Mr. Navalny’s supporters off-balance by processing his case at breakneck speed.
Images from inside the makeshift courtroom showed a judge in a black robe sitting at a simple table with a microphone, with a messy bulletin board behind her and a copy machine off to one side.
“What is happening here is impossible,” Mr. Navalny said in the video. “This is the highest degree of lawlessness — I can’t call it anything else.”
Olga Mikhailova, another lawyer for Mr. Navalny, said that his legal team would file a formal complaint about Monday’s decision. The lawyers also said that he would be held in a high-security prison in central Moscow.
Mr. Navalny, long one of Mr. Putin’s most prominent critics, collapsed and fell into a coma in August, and was airlifted to Germany for treatment. Laboratories in Germany, France and Sweden determined he had been poisoned by a military-grade nerve agent from the Novichok family, which was developed in the Soviet Union and Russia.
The opposition leader vowed to return to Russia once he recovered, and last week announced his plans to fly to Moscow, despite the threat of arrest upon arrival.
That is exactly what happened Sunday evening: After Mr. Navalny’s flight landed at Sheremetyevo Airport, police officers met him at passport control and took him into custody. He spent the night at Police Station No. 2 in Khimki, near the airport, and was denied access to his lawyer. Mr. Kobzev was not allowed into the police station until Monday morning.
“It seems that the grandpa in the bunker is so afraid of everything that they demonstratively ripped apart the code of criminal procedure and threw it in the trash,” Mr. Navalny said, using one of his epithets for Mr. Putin.
Most journalists gathered outside the police station were not being let in, but at least three pro-Kremlin news outlets were allowed to enter. The police cited Mr. Navalny’s lack of a recent coronavirus test as the reason the hearing was not held in a regular courtroom and said attendance was restricted for reasons of “sanitary-epidemiological safety.”
“I demand that this procedure be as open as possible so that all media outlets have the possibility to observe the incredible absurdity of what is happening here,” Mr. Navalny told the judge, according to another video posted by his spokeswoman.
As Mr. Navalny faced the judge inside, several hundred journalists and supporters stood in the bitter cold outside the barbed-wire fence ringing the police station, which is in a residential neighborhood of Soviet-era buildings. Some of his backers chanted “Freedom!” and “Let him go!”
Handcuffed, Mr. Navalny flashed a victory sign as he was led out of the police station after the hearing.
Some supporters of Mr. Navalny who arrived at the scene took refuge in the stairwells of nearby buildings. Irina Fokina and Sergei Fokin, a couple in their mid-30s, said they had been glued to online live-streams all Sunday evening as the drama of Mr. Navalny’s arrival unfolded.
Mr. Navalny was detained minutes after he arrived in Russia for the first time since August, when he was flown to Berlin in a coma. Russia’s prison service said that while recuperating in Germany, he had violated the terms of his suspended sentence, which require him to check in with the authorities twice a month.
“What an enormous embarrassment for the whole judicial system,” Ivan Zhdanov, the director of Mr. Navalny’s Anti-Corruption Foundation, posted on Twitter. “This is simply something incredible.”
Chancellor Angela Merkel of Germany called for the immediate release of Mr. Navalny and for Russia to examine the causes of his poisoning, her spokesman said. In the United States, both the departing and incoming administrations also called for Mr. Navalny’s release, with Secretary of State Mike Pompeo writing that “confident political leaders do not fear competing voices.”
Ursula von der Leyen, the president of the European Commission, the European Union’s executive branch, said in a statement, “The Russian authorities must immediately release him and ensure his safety.”
“Detention of political opponents is against Russia’s international commitments,” she added.
Russian officials dismissed the criticism. Mr. Lavrov, the Russian foreign minister, said that Western officials simply saw the case as a welcome distraction from their own problems.
“We are seeing how they’ve grabbed onto yesterday’s news about Navalny’s return to Russia — one can really feel how happily they’re commenting on it,” Mr. Lavrov said. “They are happy because it lets Western politicians think that they can thus distract attention from the global crisis in which the liberal model of development has ended up.”
As is often the case in Russia, historical symbolism loomed over the events on Monday. Photographs from inside the makeshift courtroom showed a portrait just behind Mr. Navalny of Genrikh Yagoda — a director of the Soviet secret police who supervised Stalin’s show trials in the 1930s and expanded the prison-camp system known as the Gulag.
On Russian state television’s marquee news show on Sunday night, the host Dmitry Kiselyov drew a different comparison, underscoring the government line that Mr. Navalny was working for Western intelligence agencies. He likened Mr. Navalny’s flight from Berlin to the sealed train that took Lenin from Switzerland, via Germany, to St. Petersburg in 1917, setting the stage for the Russian Revolution.
“The assault force isn’t quite on the same scale, but the Germans are in their repertoire,” Mr. Kiselyov said. “And everything is set up to show that they’re up to something special.”