President Joe Biden met with the leaders of Sweden and Finland at the White House Thursday after the two countries submitted applications to join NATO.

"Today I'm proud to welcome and offer the strong support of the United States for the applications of two great democracies, and two close, highly capable partners to join the strongest, most powerful defensive alliance in the history of the world," Biden said.

Biden reaffirmed the U.S.'s support for the Nordic countries' applications to join the alliance.

"Finland and Sweden make NATO stronger not just because of their capacity, but because of their strong democracies and a strong united NATO is the foundation of America's security," he said.

Biden also sent a message to Russian President Vladimir Putin and Russia.

"So let me be clear: New members joining NATO is not a threat to any nation. It never has been. NATO's purpose is to defend against aggression, that's its purpose, to defend," Biden said.

-ABC News' Karen Travers and Justin Gomez

Vadim Shishmarin, 21, is back in court, one day after he pleading guilty to killing a 62-year-old Ukrainian civilian just days into the conflict.

Shishmarin confessed to the killing Thursday morning.

The widow of the victim testified in court that her husband meant everything to her, and she thinks the Russian soldier deserves life in prison, but if he gets exchanged for any of the Azovstal defenders she wouldn’t object.

"I feel very sorry for him," she said. "But for a crime like that -- I can't forgive him."

Shishimarin could spend the rest of his life in prison.

-ABC News' Joe Simonetti

Mass shelling of the Sumy region continued from Russian territory Wednesday evening, said Dmytro Zhyvytskyy, the governor of Sumy, on Telegram.

The shelling was along the entire border between the Sumy region and Russia, according to Zhyvytskyy.

Zhyvytskyy said Ukraine responded to the shelling appropriately and no casualties were reported.

-ABC News' Joe Simonetti

Mykhaylo Podolyak, an adviser to Ukrainian President Volodymyr Zelenskyy, told Russia not to offer Ukraine a cease-fire, because it would be impossible without Russian troops' withdrawal.

"Ukraine is not interested in new 'Minsk' and the war renewal in a few years," Podolyak said in a tweet, referring to the capital of Belarus and that country's allegiance to Russia. "Until [Russia] is ready to fully liberate occupied territories, our negotiating team is weapons, sanctions and money."

-ABC News' Joe Simonetti

Jalina Porter, the State Department's deputy spokesperson, is responding to the Russian attack at a Ukraine train station that killed at least 50, saying, "We can no longer be surprised by the Kremlin's repugnant disregard for human life."

Five children were among those killed when Russian rockets struck the station in Kramatorsk in Donetsk Oblast on Friday morning, according to Ukraine's state-owned railway company. At least 100 people were injured, according to Donetsk Oblast Gov. Pavlo Kyrylenko.

Russia has denied involvement in the attack, which occurred as "thousands" of civilians fleeing the Russian invasion were at the train station waiting to be taken to "safer regions of Ukraine," according to Kyrylenko.

"Civilians are killed when they stay in their homes, and they're killed when they try to leave," Porter said. "Actions like these demonstrate why Russia did not belong on the U.N. Human Rights Council, and they also reinforce the U.S. assessment that members of Russian forces are committing war crimes in Ukraine."

Porter declined to say if the department considers the train station attack a war crime, saying, "Assessing individual criminal liability in specific cases is the responsibility of courts, as well as other investigatory bodies. But as the secretary, Secretary [of State Antony] Blinken, has said, 'Those responsible for war crimes and other atrocities committed in Ukraine will be held to account.'"

-ABC News' Conor Finnegan