With the arrest of a Wall Street Journal correspondent on Thursday, President Vladimir V. Putin signaled to the world that he was doubling down on Russia’s wartime isolation.

Russia has expelled foreign journalists in recent years, but in jailing an American reporter, Evan Gershkovich, and formally accusing him of being a spy, the Kremlin took a step with no precedent since the collapse of the Soviet Union. It was a stunningly provocative move, aimed at one of the best-known Western journalists still working inside Russia and his employer, a pillar of the American news media.

Even after Russia invaded Ukraine, Mr. Putin sought to get his message out to Western audiences, apparently betting that he could win some sympathy amid his conflict with their governments. But a long-held assumption that he is keen on trying to keep some lines of communication open with the West is now firmly obsolete.

Instead, Mr. Putin seems to have embraced a state of political, economic and cultural estrangement from the West more extreme than at any point since the end of the Cold War. It is an isolation that has arrived with dizzying swiftness, one unimaginable even as Russia built up its forces on Ukraine’s borders early last year.

“An epoch of open confrontation has begun,” Dmitri A. Muratov, the Russian newspaper editor who won a Nobel Peace Prize in 2021, said in a phone interview from Moscow. From the Kremlin’s point of view, he went on, “the louder the conflict, the better.”

Mr. Muratov, whose newspaper, Novaya Gazeta, was shut down by the Russian government last year, noted that even Soviet leaders like Leonid I. Brezhnev sought ways to dampen Western condemnation of their crackdowns on human rights. But on Thursday, he said, the Kremlin went ahead with Mr. Gershkovich’s arrest knowing that it would provoke a global outcry.

“Good — they’ll know that we’re not kidding,” Mr. Muratov said. “That’s the signal being sent by the Russian government.”

Evan GershkovichCredit…The Wall Street Journal, via Reuters

The Kremlin may continue to try to shape Western opinion in disguised ways, using intermediaries and disinformation, but it appears to have given up on swaying the mainstream news media. Mr. Gershkovich’s arrest also raises the temperature of relations with the West, and the United States in particular, as Moscow’s forces struggle on the battlefield in Ukraine, where they face ever-expanding deliveries of Western weaponry.

Last month, Mr. Putin announced that Russia would suspend participation in the New START treaty — the last surviving arms-control agreement between the two largest nuclear-armed powers. Last weekend, he said he would position nuclear weapons in Belarus, provoking an outcry from NATO.

But beyond making nuclear threats, the Kremlin’s options for how to hit back at the West have grown increasingly limited. Europe has largely managed to wean itself off its dependence on Russian energy imports, and major Western companies have largely cut ties with Russia.

That has added to the vulnerability of Western journalists working in Russia — one of the few remaining potential pressure points for the Kremlin.

During the Cold War, Western journalists were allowed to operate in the Soviet Union, but under serious restrictions. They could be expelled if they displeased the Kremlin, at times they had to send their reports through Soviet censors, parts of the country were off-limits to them, and they were routinely followed and secretly recorded by the K.G.B.

In 1986, Nicholas Daniloff, an American reporter for U.S. News & World Report, was arrested and accused of espionage — the last known case of its kind until now — which he denied. He was released 15 days later, after intense negotiation between the two governments.

Mr. Gershkovich, 31, is not the first American to be arrested in Russia in recent years. Brittney Griner, the basketball star, spent nearly 10 months in prison on drug charges last year until the United States secured her freedom by releasing Viktor Bout, a convicted Russian arms dealer. Paul Whelan, a former Marine who traveled frequently to Russia, was arrested in December 2018 and is serving a 16-year sentence for espionage; he maintains his innocence.

But Mr. Gershkovich and other Western journalists have been working in Russia with the Kremlin’s formal approval, and were granted visas and accreditation by the Foreign Ministry. Even as Russian prosecutors brought numerous cases against Russian journalists for violating strict wartime censorship laws enacted in March 2022, they had not targeted Western journalists.

The underlying message had appeared to be that despite Russia’s conflict with the West, the Kremlin still sought to keep a door open for Western news outlets. As a result, Mr. Gershkovich’s arrest caught many of those who follow Russia’s news media and politics by surprise.

“There have been so many shocks and surprises already in this year of war,” said Andrei Kolesnikov, a political analyst for the Carnegie Endowment for International Peace who is based in Moscow. “But, still, there’s absolute shock.”

Mr. Kolesnikov, like others, said Mr. Gershkovich could have been arrested to serve as a valuable hostage whom Russia could trade in the future for Russian agents arrested abroad.

But he also said that it mirrored an increasingly aggressive domestic crackdown. In another case that highlighted Russia’s ever-harsher apparatus of repression, the single father of a 13-year-old girl who got in trouble at school for drawing a pro-Ukrainian picture was sentenced to two years in prison this week. He fled Russia but has been detained in Belarus.

“Any cases, any accusations against any person are now possible on no grounds whatsoever,” Mr. Kolesnikov said.

The Kremlin left little doubt on Thursday that Mr. Putin had personally approved Mr. Gershkovich’s arrest. Hours after the Federal Security Service, the successor agency to the K.G.B., announced that the reporter had been detained “during an attempt to receive secret information,” Mr. Putin’s spokesman volunteered that the American journalist had been caught “red-handed.”

The Wall Street Journal strongly rejected the accusations against Mr. Gershkovich and said it would seek his immediate release.

The spokesman, Dmitri S. Peskov, also told reporters that other Wall Street Journal correspondents in Russia “will continue to work” if they “are carrying out normal journalistic activity” — as if to try to signal that the arrest was a one-off case.

After Mr. Gershkovich’s arrest, the White House and Antony J. Blinken, the secretary of state, issued statements reiterating the Biden administration’s position that Americans should not travel to Russia, and that those who were already in the country should leave at once.

“We condemn the detention of Mr. Gershkovich in the strongest terms,” Karine Jean-Pierre, the White House press secretary, said in a statement. The State Department, she added, “has been in direct touch with the Russian government on this matter, including actively working to secure consular access to Mr. Gershkovich.”

Mr. Putin himself said nothing about Mr. Gershkovich’s arrest on Thursday. But he has offered vague warnings in speeches of his readiness to raise tensions with the West, and has increasingly described the United States and its allies as outright enemies of Russia. In his state-of-the-nation speech last month, he declared that the West sought to destroy Russia — “to finish us off once and for all.”

“This is how we understand everything, and we will respond accordingly,” Mr. Putin said.

Konstantin Remchukov, a Moscow newspaper editor close to Kremlin officials, said he believed that after more than a year of war, Mr. Putin was now ready to sever ties with Western countries in a way he was not prepared to do in the first months of his invasion of Ukraine.

“A new reality is being formed in this phase of the conflict,” Mr. Remchukov said. “It means a final break with the West, an uncompromising one.”