MOSCOW — Undeterred by a sudden escalation in the Kremlin’s crackdown on the opposition, tens of thousands of Russians flooded Moscow’s tree-lined boulevards  today in the first mass protest against President Vladimir Putin since his inauguration in May.

Opposition leaders put the number of protesters at 120,000, while police estimated that about 20,000 showed up. The crowd appeared to be smaller than at the anti-Putin demonstrations ahead of the March presidential election, which drew as many as 100,000 people, but the turnout was still impressive in a country where such political protests had brought out no more than a few hundred people only several months ago.

After tolerating the protests through the winter, Putin has taken a tougher stance since embarking on his third presidential term, including signing a repressive new bill last week that stiffens penalties for taking part in unauthorized rallies.

Police on Monday searched opposition leaders’ apartments, carting away computers, cellphones and other personal items. They also demanded that opposition leaders come in for questioning on Tuesday, a national holiday. They were ordered to appear just an hour before the rally began, in what was widely seen as a crude attempt to scare away the protesters.

Leftist politician Sergei Udaltsov snubbed the summons, saying he considered it his duty to lead the protest as one of its organizers. He spoke at the rally and then appeared for questioning after it was over.

Anti-corruption blogger Alexei Navalny, liberal activist Ilya Yashin and TV host Ksenia Sobchak showed up for questioning in the morning. Yashin made it to the rally in time to speak at the end, but Navalny’s interrogation lasted more than six hours and then investigators drove him to his office to conduct another search.

“It’s horrible to sit here while you are having fun,” Navalny tweeted from the Investigative Committee headquarters.

Investigative Committee spokesman Vladimir Markin said police had found more than €1 million ($1.25 million) and $480,000 in cash at Sobchak’s apartment and investigators were looking into whether she had paid her taxes.

Sobchak, a glamorous 30-year-old socialite described by some as Russia’s equivalent of Paris Hilton, insisted that she had done nothing wrong and was keeping her savings at home because she doesn’t trust banks. The authorities are likely to use the piles of cash to paint the opposition as a bunch of spoiled rich kids at odds with the majority of Russia’s population.

Sobchak, the only daughter of St. Petersburg’s late mayor, a man who was Putin’s mentor, had been spared reprisals until Monday’s raid. “I never thought that we would slide back to such repressions,” she tweeted.

Braving a brief thunderstorm, protesters showed up on the central Pushkin Square ahead of the planned march and their numbers grew as they began marching down boulevards to a broad downtown avenue where the rally was held.

Police, who had clashed with protesters at the last mass anti-Putin protest, stood guard but took no action. The demonstration ended peacefully six hours after it had begun.

“Those in power should feel this pressure. We will protest by any means, whether peacefully or not,” said Anton Maryasov, a 25-year-old postgraduate student. “If they ignore us that will mean that bloodshed is inevitable.”

Another protester, 20-year-old statistics student Anatoly Ivanyukov, said his professors discouraged them from attending the protests, but this only made him and his friends more determined to take part. “It’s like when you forbid children from doing something, it makes them even more eager to come,” he said.

Two leading sources of information on opposition activities, cable television station TV Rain and Ekho Moskvy radio, saw their broadcasts interrupted Tuesday by a series of apparent hacker attacks. Industry experts said that hackers working at the Kremlin’s behest have targeted independent news websites in the past.

Tuesday’s rally was the first since the quick passage last week of a new law that raises for taking part in unauthorized protests 150-fold, to nearly the average annual salary in Russia. Tuesday’s protest had city approval, but any shift from the location and time could give police a pretext to detain protesters.

Udaltsov urged protesters to march across town after the rally to the Investigative Committee’s headquarters to demand the release of political prisoners, an action that would likely trigger a harsh police response. But there was no sign of such a march.

Many in the crowd seemed reluctant to risk arrest.

“I’m not ready to enter into a conflict with the law, even if these laws are questionable,” said Alexei Moiseyev, a student.

Opposition leader Boris Nemtsov, speaking after Udaltsov, urged the demonstrators to act within the law. “We must act in a responsible way, peacefully and calmly,” he said.

Sergei Parkhomenko, a leading journalist who helped organize Tuesday’s protest, said as demonstrators were first gathering that any unrest would play into the Kremlin’s hands.

“They would be happy to stage some kind of provocation to prove that the people are just a herd of animals and the animals are always out of control,” he said.

A big opposition rally the day before Putin’s inauguration ended in fierce clashes between police and protesters, and some opposition activists said the violence was provoked by pro-Kremlin thugs. The questioning of the opposition leaders and the raids on their homes were connected to that May 6 protest.