MOSCOW — The Kremlin mounted Russia’s most fearsome nationwide police operation in recent memory on Sunday, seeking to overwhelm a protest movement backing the jailed opposition leader Aleksei A. Navalny that swept across the country for a second weekend in a row.
But the show of force — including closed subway stations, thousands of arrests and often brutal tactics — failed to smother the unrest. People rallied for Mr. Navalny on the ice of a Pacific bay and in the thousands in cities from Siberia to the Ural Mountains to St. Petersburg. In Moscow, protesters evaded a warren of checkpoints and lines of riot police officers to march in a column toward the jail where Mr. Navalny is being held, chanting, “All for one and one for all!”
By late Sunday evening in Moscow, more than 5,000 people had been detained in at least 85 cities across Russia, an activist group reported, though many were later released. Previously unseen numbers of riot police officers in black helmets, camouflage and body armor essentially locked down the center of the metropolis of 13 million people, stopping passers-by miles from the protest to check their documents and ask what they were doing outside.
“I don’t understand what they’re afraid of,” a protester named Anastasia Kuzmina, a 25-year-old account manager at an advertising agency, said of the police. Referring to the peak year of Stalin’s mass repression, she added, “It’s like we’re slipping into 1937.”
But the show of force also made it clear that Mr. Putin has no plans to back down. Shortly after the American secretary of state, Antony Blinken, condemned “the persistent use of harsh tactics against peaceful protesters and journalists,” Russia’s Foreign Ministry released a statement accusing the United States of backing the protests as part of a “strategy to contain Russia.”
The next test for both sides will come on Tuesday, when Mr. Navalny faces a court hearing over alleged parole violations related to a six-year-old embezzlement case that could send him to prison for several years. Mr. Navalny’s allies — some of whom helped steer the rallies from outside the country via Twitter, Telegram and YouTube — declared Sunday’s demonstrations a success and quickly called for more protests outside the courthouse on Tuesday.
“Russia’s citizens again showed their power and strength, and there’s no question that Putin understands this,” Leonid Volkov, a top aide to Mr. Navalny coordinating the protests from abroad, said Sunday in a live YouTube broadcast.
But the police sought to project their strength not only in numbers but also with more fear-inducing tactics. Video footage taken in Moscow and St. Petersburg showed people who did not appear to be resisting arrest screaming after the police used taser-like devices against them — weapons not reported to have been used at previous protests. There were also reports of tear gas having been used in St. Petersburg.
The crackdown on protesters showed that Mr. Putin — who has maintained a modicum of freedoms in the country, including an open internet and some independent news media — is ready to ratchet up authoritarianism in order to avert a possible threat to his power. The question is whether more Russians will actively resist such an authoritarian turn, especially as images of police brutality course through social media in the coming days.
“The bolts are tightening,” said Nikolai Babikov, 31, a computer systems analyst in Moscow, gazing apprehensively at the riot police and at the chunky gray police vans that hold detainees. “Freedom is being eliminated, and bit by bit we are becoming the Soviet Union again.”
Mr. Putin has faced growing discontent in the general public for several years amid a decline in real incomes and the dissipation of the patriotic fervor that accompanied his annexation of Crimea in 2014. Mr. Navalny has long been the Kremlin’s loudest critic, and he accused Mr. Putin of trying to kill him via a nerve-agent attack last summer.
Mr. Navalny put a match to that built-up discontent two weeks ago when he flew home to Moscow after five months of recovering in Germany from the poisoning, despite facing near-certain arrest upon arrival. Then, with Mr. Navalny in jail, his team released a two-hour-long video accusing Mr. Putin of having a secret palace built for him on the Black Sea.
The video was seen more than 100 million times on YouTube and energized the protests calling for Mr. Navalny’s release. On Sunday, footage from across the country showed some protesters brandishing toilet brushes and chanting, “Aqua disco” — references to an $850 toilet brush and elaborate fountain detailed in Mr. Navalny’s report.
The Kremlin has denied the report about the palace and scrambled to contain the public outrage over it. On Saturday, state television broadcast an interview with a friend of Mr. Putin, Arkady Rotenberg, who said he was in fact the owner of the property and was planning to turn it into a hotel.
“I am for honesty, nothing else,” said Lyudmila Mikhailovna, an 83-year-old retired pediatric doctor in Moscow who declined to give her last name.
She said she was no great fan of Mr. Navalny but had come out to protest after watching his video about the palace.
Sunday’s protests began around noon on Russia’s Pacific coast and rolled across the nation, with its 11 time zones, from east to west. In Vladivostok, a port city on the Sea of Japan, protesters avoided a city center blocked by riot police officers and descended onto the ice covering Amur Bay. Clasping hands, videos showed, they formed chains and danced as they chanted, “Putin is a thief!” and “Russia will be free!”
Riot officers, initially hesitant to follow on the frozen water, decided to give chase. But it seemed to be a slow-motion chase, with each side moving gingerly on the snow-covered expanse of ice under a gray late-afternoon sky.
It was just one of many remarkable scenes that played out on Sunday in eastern Russia, where large-scale protests are rare. In the Siberian city of Irkutsk, where temperatures approached minus 20 Fahrenheit, the turnout was significantly smaller than the thousands who protested last weekend — and the police presence even more imposing.
Aleksei Zhemchuzhnikov, a civic activist, said chains of riot police officers with full body armor and shields were deployed for the first time, cordoning off sections of the city center. Mobile internet access was cut off, he said.
“For Irkutsk, this was a first,” Mr. Zhemchuzhnikov said of the police response. “They were scared.”
Still, no signs have emerged of support for the protesters within the government, the Parliament, big business or the security services, which all remain firmly in Mr. Putin’s grasp. Fissions in the elite, nowhere to be seen at least on the surface in Russia, have been pivotal in the success of street movements in other former Soviet states.
In Moscow, Mr. Navalny’s team guided protesters on an evasive, zigzagging route to avoid police barricades. It encouraged them to stay together, in larger and harder-to-arrest crowds. Well before the protests began, the police sealed off much of the city center to pedestrians and shut down subway stops around the Kremlin — a crowd-control tactic used for the first time in recent years.
“Try not to leave the major streets and stay in large groups,” Mr. Navalny’s team instructed the protesters, using the messaging app Telegram. “Remember, the more of us there are, the more difficult it is for police to do anything.”
The mainly young protesters, following the Navalny social-media accounts on their phones, in many cases turned and followed the team’s directions — which led them toward the jail where Mr. Navalny was being held. The police, wielding shields and batons, tried to break the crowd into smaller groups and detain protesters after pushing them into walls and fences.
In chaotic scenes, police officers arrested people trying to hide in backyards and in the entryways to apartment buildings. By early evening, the Tass state news agency reported that the police were checking courtyards and apartment buildings for stragglers.
The harsher tactics were redolent of the protests in Belarus, where President Aleksandr G. Lukashenko used fierce police might to put down demonstrations after fraudulent elections last summer. The Russian police on Sunday did not use Mr. Lukashenko’s toughest methods — which included stun grenades and rubber bullets — but they seemed to echo his strategy of defusing dissent not by dialogue, but by brute force.
In St. Petersburg, a reporter for the newspaper Novaya Gazeta posted a video of police officers dragging an unconscious protester into a police van after a “harsh detention.” Reports of officers in plain clothes beating protesters surfaced in two provincial cities, Kursk and Volgograd.
On Moscow’s grand Garden Ring, the city center’s main circular thoroughfare, Lyudmila Mikhailovna, the retired pediatrician, glowered at the phalanx of burly officers in front of her.
She said that she had been going to protests since the Gorbachev era, but that, despite repeated disappointment, would continue to “so that my children and grandchildren don’t have to live in a greedy police state.” She added, “Things now are just intolerable.”
Oleg Matsnev and Sophia Kishkovsky contributed research.
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