BERLIN — The head of the North Atlantic Treaty Organization said Sunday that the security bloc would grant fast-track membership to Sweden and Finland, raising the pressure on Vladimir V. Putin, who justified his invasion of Ukraine by what he cast as the need to keep the military alliance away from Russia’s borders.
“President Putin wants Ukraine defeated, NATO down, North America and Europe divided,” the NATO secretary general, Jens Stoltenberg, said in Berlin after meeting the foreign ministers of the alliance’s members. “But Ukraine stands, NATO is stronger than ever, Europe and North America are solidly united.”
Both countries said their applications were imminent. Finland’s Parliament is expected to ratify a NATO application on Monday. And Sweden’s governing Social Democratic Party said Sunday that it would vote in favor of joining NATO — all but guaranteeing that the Nordic nation would end 200 years of neutrality.
The possibility of NATO troops deploying along Russia’s 810-mile border with Finland comes as Mr. Putin is facing notable setbacks in the war he began in Ukraine nearly three months ago.
Ukrainian forces have advanced to near the Russian border in recent days after pushing Russian troops from the outskirts of Kharkiv, Ukraine’s second-largest city. And evidence mounted on Sunday that Russia’s offensive in the Donbas region further east is faltering after the initial modest gains.
Estimates based on publicly available evidence suggest that well over 400 Russian soldiers were killed or wounded as they tried to cross the Donets River at the village of Bilohorivka, in the eastern Luhansk region, in a bid to encircle Ukrainian forces. The debacle is likely to have been one of the bloodiest engagements since the start of the war, leading even influential pro-Russian bloggers to begin to voice concern, despite the Kremlin’s efforts to criminalize dissent.
“I’ve been keeping quiet for a long time,” Yuri Podolyaka, a war blogger with 2.1 million followers on the messaging app Telegram, said in a video posted on Friday, saying he had avoided criticizing the Russian military.
“The last straw that overwhelmed my patience,” he said, “was the events around Bilohorivka, where due to stupidity — I emphasize, because of the stupidity of the Russian command — at least one battalion tactical group was burned, possibly two.”
British intelligence officials said Sunday that Russia had lost a third of the ground forces it had committed to the Ukraine offensive. The rate of attrition, if confirmed, would make it extremely difficult for Russia to achieve a decisive victory against a well-motivated and increasingly well-armed and trained enemy, according to analysts.
But within Russia, the Kremlin’s propaganda and repression of independent media have effectively shielded the majority of the population from the true human cost of the war. The Russian government’s emergency economic measures have thus far blunted the impact of sanctions.
Western and Ukrainian officials say that thousands of Russian soldiers have already died in the conflict. But reports about deaths have been heavily censored by the state and concentrated among working-class families spread across the world’s largest country, precluding local tragedies from coalescing into national grieving.
Many Russians believe the war is no longer against Ukraine, but has morphed into a proxy conflict with the United States and NATO, who, they say, are exploiting the conflict to destroy their nation, according to interviews with a half-dozen residents in Moscow and in provincial Siberia.
If pushed into a corner, Russia will always fight on, some of them said, even if it risks provoking a nuclear war.
The decision of Finland and Sweden to apply to join NATO has only played into the siege narrative pushed by the Kremlin, tapping into patriotic feelings in a nation that prides itself on coming together to repel foreign threats over the centuries.
For their part, both Nordic states have long been wary of Russian power.
Finland was part of the Russian Empire and fought to maintain its independence from the Soviet Union during the Second World War. Sweden and Russia fought to dominate Eastern Europe in the 18th century.
But Finland and Sweden both remained neutral after the Soviet Union confronted the United States and its allies in the aftermath of the Second World War. The end of that neutrality is a striking sign of the extent to which Mr. Putin’s strategic calculation in Ukraine has backfired and undermined longstanding Russian security priorities.
Russia-Ukraine War: Key Developments
Inching closer to NATO. Finland’s government announced that the nation would apply for NATO membership, hours before Sweden’s governing party said that it also supported joining the alliance. If accepted into NATO, both nations would set aside a long history of military nonalignment.
McConnell visits. Senator Mitch McConnell of Kentucky, the minority leader, visited Ukraine with three other senior Republican senators to meet with President Volodymyr Zelensky. The secret visit comes as Senate leaders are working to pass a $40 billion aid package for Ukraine.
On the ground. Russia has “lost momentum” in its campaign to seize Ukraine’s eastern Donbas region, Britain’s Defense Ministry said in a report. The agency said that Moscow “has now likely suffered losses of one-third of the ground combat forces it committed in February.”
As a rationale for his invasion of Ukraine, Mr. Putin had said he was concerned about NATO enlargement, and in particular the deployment of new missiles near the Russian borders. This concern is shared by the majority of Russian citizens, who believe the United States has taken advantage of their country’s weakness after the collapse of the Soviet Union to bring missiles to its borders.
An application to join NATO must be unanimously approved by its 30 members. One of those members, Turkey, has raised issues over the pending applications, though it has suggested it would not oppose admission if its own security concerns are addressed.
Antony J. Blinken, the American secretary of state, said after the Berlin meetings on Sunday that there was strong support among current NATO members on bringing the two Nordic states into the alliance. U.S. officials said their application processes should be completed in months, and Germany’s foreign minister, Annalena Baerbock, said Sunday that her nation would be among the first to ratify them.
The Baltic States joined NATO in 2004, bringing the alliance to the border with the Russian heartland. And in 2008, President George W. Bush promised that Ukraine and Georgia could enter NATO and pushed the alliance to make similar statements.
Western European nations, however, were reluctant to make good on that promise. Before the war, both the United States and European allies had said that Ukraine would not be qualified to enter NATO anytime soon.
After Russia invaded, Ukraine’s president, Volodymyr Zelensky, pushed for the Western powers to act on his government’s desire to enter NATO, but has since said he would be more open to a neutral Ukraine if its security is guaranteed.
On Sunday morning, Mr. Blinken met in Berlin with Dmytro Kuleba, the foreign minister of Ukraine, to discuss the war. The State Department said the two men discussed the details of further American security assistance to Ukraine.
Mr. Kuleba posted on Twitter a photo of the two standing in a room and smiling. “More weapons and other aid is on the way to Ukraine,” he wrote.
Edward Wong reported from Berlin, and Anatoly Kurmanaev from Mexico City. Reporting was contributed by Anton Troianovski from New York; Carlotta Gall from Prudyanka, Ukraine; Ivan Nechepurenko from Tbilisi, Georgia; and Marc Santora from Krakow, Poland.