Here’s what we know about the Moskva, Russia’s sunken warship.

However, if Mariupol falls, Russia will be able to claim the land route from Crimea that it seeks. It could then send reinforcements to the eastern Donbas region, where it is now concentrating troops for what analysts predict will be a major offensive.

But Russia’s setbacks are real, leaving President Vladimir V. Putin so desperate for a victory that he could potentially turn to limited nuclear weapons, the director of the C.I.A. warned on Thursday.

The European Union, which earlier this month banned Russian coal for the first time, is now likely to adopt a similarly phased ban of Russian oil, E.U. officials and diplomats said. Mr. Putin acknowledged on Thursday that the Western sanctions already in place had hurt his country’s vital energy sector.

In other developments:

• Dmitri A. Medvedev, a senior Russian security official, said on Thursday that if Sweden and Finland joined NATO, there would be “no more talk of a nuclear-free Baltics” region.

• Two American lawmakers, both Republicans, became the first American officials to visit Kyiv on Thursday. The Biden administration is considering sending a high-level official to the city, according to a person familiar with the internal discussions, but has yet to publicly name anyone.

That body of water, whose coastline is shared with several other countries, including Ukraine, Georgia and Turkey, has been of strategic importance to Russia for centuries.

The Moskva was deployed to support Russian aircraft and troops in Syria in 2015, and in 2008, it patrolled the coast of Georgia during the Russian-Georgian war.

Since Russia invaded Ukraine in February, the Moskva — armed with 16 Vulkan missile launchers with a strike range of more than 400 miles, according to Russian state media — and the rest of the Black Sea fleet have launched missiles into Ukraine several times. The ships also cut off Ukraine’s access to the sea and the economic lifeline it provided.

Although military analysts said the loss of the Moskva was not likely to alter the course of the war, it was an embarrassment for Russia’s military, which has spent billions of dollars to modernize its weaponry.

The ship had the ability to do “significant damage” in the Black Sea, said Gary Roughead, a retired admiral and the former chief of naval operations for the United States. He added that with the Moskva’s demise, Russia has most likely lost a key communications and controls platform.

The loss of the Moskva has been estimated by Forbes Ukraine to have cost Russia $750 million and to be Russia’s most expensive military loss in the war to date.

The vessel was also a symbol of national pride. Its name was “Glory” when it was first put into service for the Soviet Navy in the early 1980s. It was renamed after the Russian capital in 1996, according to Russian state media.

“Picture the aircraft carrier USS George Washington going to the bottom of the Pacific Ocean,” James Stavridis, a retired U.S. Navy admiral and a former supreme allied commander at NATO, said of the ship’s symbolism.

“It’s a significant hit to their prestige to lose something like that,” said Admiral Roughead, adding, “It calls into question the readiness of the fleet.”

The Moskva is the same ship, Ukrainian officials have said, that was famously and obscenely told off by Ukrainian border guards on Snake Island in February.

The Russian Ministry of Defense has said that all crew members on the Moskva — which usually number around 500 — had been evacuated. The ship will now join an unknowable number of other vessels, some more than a millennium old, on the floor of the Black Sea.

James Glanz contributed reporting.

That has certainly been true for Ms. Smirnova, 30. As the war got worse, and dissent in Russia was ruthlessly quashed, Ms. Smirnova, who had gone to Dubai to recover from a knee injury, realized that she could no longer return home. “If I were to go back to Russia, I would have to completely change my opinion, the way I felt about the war,” Ms. Smirnova said in a recent interview in Amsterdam, adding that returning would be, “quite frankly, dangerous.”

So she left the Bolshoi, the storied company whose name is synonymous with ballet, with its gilded theaters just blocks from the Kremlin, uprooted her life and moved to Amsterdam, where she joined the Dutch National Ballet.

The departure of Ms. Smirnova is a blow to the pride of a nation where, since the days of the czars, ballet has had an outsize importance as a national treasure, a leading cultural export and tool of soft power.

Her move is one of the most visible symbols of how Russia’s invasion of Ukraine has upended ballet, as prominent artists shun Russia’s storied dance companies; theaters in the West cancel performances by the Bolshoi and the Mariinsky; and dance in Russia, which had opened up to the world in the decades since the collapse of the Soviet Union, seems to be turning inward again.

But when it came to talking about World War II, this is what he said: “The real disaster started when the Russians invaded. The Russians were worse than the Germans.”

“The Germans,” he said, “did not hurt ordinary people.”

My first reaction fell somewhere between disappointment and silent outrage: How could this farmer be so kind and so blind? How could he say the Germans didn’t hurt “ordinary people” when they murdered millions of Jews right here in Poland? The biggest death camps were in Poland, and the more I thought about it, the more I was shocked by what the farmer said.

But then I realized he and I were actually engaging in a similar type of thinking.

He couldn’t stop obsessing about Russia, which occupied Poland during World War II and controlled it for many decades afterward, and is now dropping bombs just a few miles from the border. And I couldn’t stop thinking about the Holocaust. Neither of us had lived through all that history ourselves — the trauma was handed down to us from our families — but both of us were trapped in the past.

There is a saying in the high Arctic that if your snowmobile breaks down, no one asks for your nationality before helping to repair it. But Russia’s invasion of Ukraine has echoed at the top of the world, threatening longstanding personal and professional relationships, cultural interactions and even friendly sports rivalries.

The Svalbard tourist board has called for a boycott of Russian state-owned businesses in the coal mining settlement of Barentsburg. Mr. Gushchin, until now considered an inclusive, moderating figure, has surprised and angered many with comments concerning the Russian invasion and an accusation that Norwegian news media provide mostly “fake news.”

The train that delayed Mr. Csoma’s drive home was not only unusually long but also signaled a singular escalation in Western efforts to help Ukraine defend itself. It carried an air defense system made up of 48 surface-to-air missiles, four launchers and radars to guide the rockets to their targets, which in Ukraine means Russian warplanes and missiles.

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As President Vladimir V. Putin of Russia vows to fight the war to its “full completion” and his forces regroup for an expected push in Ukraine’s east, NATO countries, including the United States, are scrambling to keep the weapons flowing and bulk up the country’s defenses.

Bolstering Ukraine’s long-range air defense capabilities is seen as especially critical. Ukraine already had its own S-300 and other air defense systems, but some of these have been destroyed, leaving Russia with a large degree of freedom to hit Ukrainian targets from the air with warplanes and cruise missiles.

Increasingly desperate to reverse this imbalance, President Volodymyr Zelensky of Ukraine has repeatedly pleaded with NATO to “close the sky over Ukraine” by imposing a no-fly zone. But NATO has been unwilling to send its own warplanes into Ukraine.

Instead, the United States offered Slovakia, a fellow NATO member, a substitute battery of American-made Patriot missiles if it would “donate” its aging S-300 system to Ukraine.

Given the enormous security requirements for the president or vice president in a war zone, it is unlikely that either Mr. Biden or Vice President Kamala Harris would travel to the barricaded Ukrainian capital, U.S. officials say. But another top official, such as Secretary of State Antony J. Blinken or Defense Secretary Lloyd Austin, might more easily make the symbolic trip.

Spokesmen for both Mr. Blinken and Mr. Austin on Thursday said they had no travel plans to announce. At a daily press briefing, however, the State Department spokesman, Ned Price, noted that Mr. Blinken speaks several times a week to his Ukrainian counterpart, Dmytro Kuleba. Mr. Price also noted that the men have met in person twice since Russia invaded Ukraine: last week at NATO’s headquarters in Brussels and at the Ukraine-Poland border last month.

The Russian retreat from the Kyiv area and recent visits to the capital by European leaders, including a surprise weekend trip by the British prime minister, Boris Johnson, have prompted discussions about sending a senior American there to demonstrate U.S. support.

Such a trip would involve challenging logistics. British media reported that Mr. Johnson traveled by a combination of car, train, helicopter and military plane.

Mr. Price also said that U.S. diplomats who were evacuated from Ukraine in February remain across the border in Poland. He said the United States was “constantly evaluating and re-evaluating the safety and the security situation” in Ukraine and hoped to restore a diplomatic presence there “as soon as it would be safe and practical to have U.S. diplomats on the ground there.”

“In stormy sea conditions, the ship sank,” the Defense Ministry said in a short statement, according to Russian news agencies.

The loss of one of the Russian Navy’s largest and most powerful ships, named after the Russian capital, was a major setback for the Kremlin and a victory for Ukraine as the 50-day-old war appeared to be entering a new phase. Russia has massed troops in the country’s east and appears to be poised for a new offensive there after withdrawing from the north and the region around the capital, Kyiv.

Ukrainian officials had said their forces hit the ship with missiles, but Moscow acknowledged only the fire and the detonation of ammunition. Dmitri S. Peskov, the Kremlin’s spokesman, said earlier on Thursday that President Vladimir V. Putin had been briefed on the situation.

The ship could carry 16 long-range cruise missiles and typically had a crew of about 500 sailors. It was also outfitted with modern air defense systems, making its loss — if Ukraine did indeed strike the ship — an embarrassment for Russia’s military, which has invested billions of dollars into modernizing its weaponry.

If the loss of the ship stemmed from an accidental fire, as the Defense Ministry suggested, the episode would become one of the most striking examples of the miscues and poor discipline that appear to have plagued Russia’s invasion from the start.

The Russian Defense Ministry did not acknowledge any casualties, asserting in its statement that the ship’s crew had been evacuated to “ships of the Black Sea fleet that were in the area.” There was no independent confirmation of that claim.

On Tuesday, the head of Odesa’s military forces, Maxim Marchenko, said on Telegram that Ukrainian forces had struck the ship with anti-ship Neptune missiles.

Although military analysts said the loss of the ship was not likely to alter the course of the war, it was likely to offer a morale boost for Ukrainian forces. In addition, an attack by the Neptune missile systems, if confirmed, would be a significant sign of Ukraine’s military capability and could serve as a deterrent to other Russian naval attacks.

Though Moscow has not confirmed the ship was hit by missiles, a half dozen other Russian ships in the Black Sea moved farther away from the Ukrainian coast on Thursday, a senior U.S. defense official said on Thursday, lending credence to the claim.

For its part, Ukraine seized the opportunity to mock the invader.

“Russian warship, what are you sinking?” the government wrote on Twitter.

In announcing the move, which would freeze assets estimated to be worth up to £10 billion, or roughly $13 million, the U.K. government said it amounted to “the largest asset freeze action in U.K. history.”

“We are tightening the ratchet on Putin’s war machine and targeting the circle of people closest to the Kremlin,” said Liz Truss, Britain’s foreign secretary. “We will keep going with sanctions until Putin fails in Ukraine. Nothing and no one is off the table.”

The new measures also include a travel ban on Mr. Davidovich.

Mr. Tenenbaum is listed as a director on Chelsea Football Club’s website. The British announcement states that Mr. Tenenbaum took control of Ervington Investments Ltd., an investment company tied to Mr. Abramovich, shortly after Russia’s invasion of Ukraine in February. Mr. Davidovich then took over the company from Mr. Tenenbaum in March, according to the announcement.

The club declined to comment on the new sanctions.

European countries have been stepping up sanctions against Russia in recent days, and are also considering a larger ban on Russian oil imports, a step they have been reluctant to take because of the potential for a wider impact on the global economy.

Earlier in the week, authorities in Jersey, a British territory, froze $7 billion in assets believed to be tied to Mr. Abramovich.

The French government published a list this week of dozens of properties, many of them on the French Riviera, that it said it would be freezing as part of its sanctions on Russia. While the owners of the assets can still access the properties, they are forbidden to sell or rent them.

In Germany, authorities recently announced the seizure of the superyacht Dilbar after determining that it was tied to Alisher Usmanov, a Russian oligarch, according to The Associated Press. The United States previously targeted Mr. Usmanov in a batch of sanctions announced last month that designated the superyacht as blocked property, estimating its value to be between $600 and $735 million and noting that it was one of the world’s biggest superyachts, outfitted with two helipads and an indoor pool.

Aurelien Breeden contributed reporting from Paris.