Finland on Sunday confirmed its bid for Nato membership as a bulwark against Russia, redrawing the balance of power in Europe after decades of military non-alignment.
In Helsinki, President Sauli Niinisto called the move “historic”.
“A new era is opening,” he said, before the decision is put before parliament for approval.
Finland's move, expected to be followed by neighbouring Sweden, has angered the Kremlin, which insists the Nordic nations have nothing to fear and promised reprisals.
Russia has already pulled the plug on electricity supplies to Finland, with whom it shares a 1,300-kilometre (800-mile) border, prompting grid bosses to ask Sweden for back-up.
The announcement came as Western intelligence claimed that Russia has suffered huge military losses in Ukraine and that it will get bogged down in the strategic east as it faces stiff resistance.
And away from the conflict, Ukraine was basking in the morale-boosting glory of the landside win of its entry to the Eurovision Song Contest, the world's biggest live music event.
On the battlefield, Russia's defence ministry claimed it had carried out “high-precision” missile strikes on four artillery munitions depots in the Donetsk area in the east of Ukraine.
Airstrikes had also destroyed two missile-launching systems and radar, while 15 Ukrainian drones were taken out around Donetsk and Lugansk, it added.
The claims came as UK defence chiefs said Russia's offensive in the Donbas region had “lost momentum”.
Demoralised Russian troops had failed to make substantial gains and Moscow's battle plan was “significantly behind schedule”, UK Defence Intelligence said in an update.
Also read: Moscow warns Finland over Nato designs
“Russia has now likely suffered losses of one third of the ground combat force it committed in February.
“Under the current conditions, Russia is unlikely to dramatically accelerate its rate of advance over the next 30 days.” Exact, reliable casualty figures have been hard to come by, with Ukraine and Russia regularly publishing claims of enemy dead.
Kyiv says its troops have killed nearly 20,000 Russian military. Moscow on March 25 said its forces had killed at least 14,000 Ukrainian military personnel.
But both figures are widely suspected to be inflated, and have not been verified by AFP or independent conflict monitors.
The Kremlin said in late March that some 1,351 of its troops had been killed.
A senior Nato military official estimated at the same time that between 7,000 and 15,000 Russian soldiers could have been killed in the fighting up to that point.
Russia has increasingly turned its attentions to eastern Ukraine after failing to capture Kyiv.
Western leaders have predicted a drawn-out war of attrition stretching into next year, but Ukrainian commanders have been more upbeat and predicted a turning point by August.
Russia has been trying to cross a river and encircle the city of Severdonetsk, according to the governor of the eastern Lugansk region.
But Serhiy Gaidai said Ukrainian forces had repelled the push.
Aerial images showed dozens of destroyed armoured vehicles on the river bank and wrecked pontoon bridges.
Local officials in Ukraine's second city of Kharkiv in the north have said Russian troops were withdrawing, and Ukrainian forces were counter-attacking.
Ukrainian troops have been fighting a rearguard battle from a network of underground tunnels and bunkers in the bowels of a steelworks in the devastated southern port city of Mariupol.
Families of the estimated 600 troops still holed up at the Azovstal plant and facing heavy bombardment have appealed to China to intervene to secure their release.
The United Nations and Red Cross helped to evacuate women, children and the elderly from the plant whey there were sheltering earlier this month.
Petro Andryushchenko, an adviser to the mayor of the city, said on Telegram that a “huge convoy” of 500 to a thousand cars had arrived in the city of Zaporizhzhia.
In war-weary Kyiv, news of Ukraine's runaway Eurovision success was met with outpourings of joy and relief, bringing some respite from a daily barrage of grim reports of the conflict.
“It's a small ray of happiness. It's very important now for us,” said Iryna Vorobey, a 35-year-old businesswoman, adding that the show of support from across Europe was “incredible”. “I'm very glad,” said Andriy Nemkovych, a 28-year-old project manager.
“This win is so very good for our mood.” The Kalush Orchestra's “Stefania”, a rap lullaby combining folk and modern hip-hop rhythms, won the popular vote of viewers, pushing the UK into second place.
President Volodymyr Zelensky praised the group, whose lyrics about home took on extra poignancy with six million Ukrainians currently displaced outside the country.
“Our courage impresses the world, our music conquers Europe!” he wrote on Facebook. But others greeted the victory with more tepid emotions.
“Now, it's not the most important thing,” said Vadym Zaplatnikov, 61, who insisted that “having Crimea back” would be a much more welcome announcement.