MOSCOW — From the frozen streets of Russia’s Far East and Siberia to the grand plazas of Moscow and St. Petersburg, tens of thousands of Russians rallied in support of the jailed opposition leader Aleksei A. Navalny on Saturday in the biggest nationwide showdown in years between the Kremlin and its opponents.
The demonstrations did not immediately pose a dire threat to President Vladimir V. Putin’s grip on power. But their broad scope, and the remarkable defiance displayed by many of the protesters, signaled widespread fatigue with the stagnant, corruption-plagued political order that Mr. Putin has presided over for two decades.
The protests began to unfold in the eastern regions of Russia, a country of 11 time zones, and they moved like a wave across the nation despite a heavy police presence and a drumbeat of menacing warnings on state media to stay away.
On the island of Sakhalin, just north of Japan, hundreds gathered in front of the regional government building and chanted, “Putin is a thief!” The protests spread to the sub-Arctic city of Yakutsk, where it was minus 60 degrees Fahrenheit, and to rallies attended by thousands in cities across Siberia. Hours later, as night fell in Moscow, people pelted the police with snowballs and kicked at a car belonging to the domestic intelligence agency.
By late evening in Moscow, more than 3,000 people had been arrested in at least 109 cities, according to OVD-Info, an activist group that tracks arrests at protests.
Mr. Navalny’s supporters claimed success and promised more protests next weekend — even though many directors of his regional offices had been arrested.
“If Putin thinks the most frightening things are behind him, he is very sorely and naïvely mistaken,” Leonid Volkov, a top aide to Mr. Navalny, said on a live broadcast to YouTube from an undisclosed location outside Russia.
The protests came six days after Mr. Navalny, a 44-year-old anti-corruption activist, was arrested upon his arrival in Moscow on a flight from Germany, where he had spent months recovering from poisoning by a military-grade nerve agent. Western officials and Mr. Navalny have described the poisoning, which took place in Siberia in August, as an assassination attempt by the Russian state. The Kremlin denies this.
Mr. Navalny, who now faces a yearslong prison term, called on his supporters across the country to take to the streets this weekend, even though officials did not authorize protests. Russians responded with the most widespread demonstrations that the nation has seen since at least 2017 — numbering in the tens of thousands in Moscow and St. Petersburg and in the thousands in each of several cities to the east, including Yekaterinburg, Novosibirsk, Tomsk, Omsk and the Pacific port of Vladivostok.
“There was this heavy feeling that Russian public opinion had hardened in cement, as though it was stuck in a dead, hidebound ball,” said Vyacheslav Ivanets, a lawyer in the Siberian city of Irkutsk who took part in the protests. “Now I feel that the situation has changed.”
Mr. Navalny, long Mr. Putin’s loudest domestic critic, has used his populist touch on social media and humorous, tough and simple language to emerge as Russia’s only opposition leader commanding a following across a broad cross-section of society. His status among Putin critics rose further in recent months when he survived the nerve-agent attack and then returned home to Russia even though he was facing near-certain arrest.
That arrest on Sunday, protesters said, helped unleash pent-up discontent over economic stagnation and widespread official corruption under Mr. Putin.
But Mr. Putin’s Kremlin has outlasted protests before — and there was little immediate indication that this time would be different. Russia’s state media quickly made it clear that there was no chance the Kremlin would buckle under pressure, condemning the protests as a nationwide “wave of aggression” that could lead to prison terms against some participants.
“Attacking a police officer is a criminal offense,” a state television report said. “Hundreds of videos were shot. All the faces are on them.”
In Washington, the State Department said on Saturday that it “strongly condemns the use of harsh tactics against protesters and journalists” in Russia. The Russian Foreign Ministry countered by claiming that the United States had helped “incite radical elements” to join the unauthorized protests and that American officials were “facing a serious talking-to” by Russian diplomats.
Some protesters acknowledged that, despite the significance of Saturday’s protests, it would take far greater numbers to change the course of the nation’s politics. In neighboring Belarus, many more people protested for weeks last year against the authoritarian president, Aleksandr G. Lukashenko — a close ally of Mr. Putin’s — without unseating him.
“I’m a bit disappointed, honestly,” said Nikita Melekhin, a 21-year-old a nurse in Moscow. “I was expecting more.”
On the streets, the police presented a monumental show of force, but largely refrained from large-scale violence. At Pushkin Square in central Moscow, the focal point of the rally in the capital, baton-wielding riot police repeatedly rushed the crowd to try to disperse it, but avoided using tear gas or other more violent crowd-control methods.
They arrested most of Mr. Navalny’s top associates beforehand and detained his wife, Yulia Navalnaya, at a protest on Saturday before releasing her hours later.
Still, videos circulating on social media captured remarkable clashes between protesters and the police — an indication of a new fearlessness among some Russians and of the uncertainty of what lies ahead. In several cases, protesters could be seen pelting the police with snowballs, even though prosecutors have in the past sought yearslong prison sentences for people who threw objects at officers.
Chanting “shame” protesters in Moscow also threw snowballs at a passing government car. After it came to a stop, people rushed at the car, which belongs to Russia’s domestic intelligence agency, and started kicking it. The driver suffered an eye injury in the attack, the state news media reported later.
The state news media reported that at least 39 Moscow law-enforcement officers were injured in Saturday’s events. There were also videos of officers viciously beating and kicking individual protesters, including outside the Moscow jail where Mr. Navalny has been confined.
The question now is whether the intensity of the clashes will further galvanize Russians — or end up dissuading them from heeding the Navalny team’s call for more protests.
Opinion polls in recent months — of uncertain value in a country saturated by state propaganda and where people are often fearful of speaking out — have indicated that Mr. Putin faces no grave challenge to his popularity from Mr. Navalny, whose name has never been allowed to appear on a presidential ballot. Mr. Putin refuses to utter his name in public.
A November survey by the Levada Center, an independent and highly respected polling organization, found that only 2 percent of respondents named Mr. Navalny as their first choice when asked whom they would choose if a presidential election were to be held the following Sunday. Fifty-five percent named Mr. Putin.
Nevertheless, Mr. Navalny’s dramatic return to Russia last Sunday — and his video report about Mr. Putin’s purported secret palace, which has been viewed more than 70 million times on YouTube — have raised the opposition leader’s prominence across the country.
“I was never a big supporter of Navalny, and yet I understand perfectly well that this is a very serious situation,” Vitaliy Blazhevich, 57, a university teacher, said in a telephone interview about why he had gone out to rally for Mr. Navalny in the city of Khabarovsk on the Chinese border.
“There’s always hope that something will change,” Mr. Blazhevich said.
Vasily Zimin, a 47-year-old partner in a Moscow law firm, trudged through slush and said he had come to protest the rampant corruption during Mr. Putin’s time in power.
“How can you say, ‘I can’t take any more of this’ while sitting on your couch?” he said.
Ivan Nechepurenko and Andrew E. Kramer contributed reporting from Moscow. Oleg Matsnev and Sophia Kishkovsky contributed research.