Russia-Ukraine updates: 2 US veterans who joined Ukrainian forces missing

In a phone call initiated by Finland on Saturday, Russian President Vladimir Putin and Finnish President Sauli Niinisto discussed Finland’s decision to join NATO.

Putin described the decision as a mistake that could damage relations between their two countries, according to the Kremlin.

"Putin stressed that abandoning the traditional policy of military neutrality would be wrong, since there are no threats to Finland's security. Such a change in the country's foreign policy course may negatively affect Russian-Finnish relations, which for many years have been built in the spirit of good-neighbourliness and partnership, and have been mutually beneficial," the Kremlin said.

Niinisto's office said Finland initiated the call.

""President Niinisto told President Putin how fundamentally the Russian demands in late 2021 aiming at preventing countries from joining NATO and Russia’s massive invasion of Ukraine in February 2022 have altered the security environment of Finland," Niinisto's office said in a statement.

Niinisto told Putin that every independent nation maximizes its security, according to Niinisto's office.

“The conversation was direct and straight-forward and it was conducted without aggravations. Avoiding tensions was considered important," President Niinisto says.

-ABC News' Somayeh Malekian

U.S. senators, including Senate Minority Leader Mitch McConnell visited Kyiv, Ukrainian President Volodymyr Zelenskyy announced in a video posted online Saturday.

“The visit of the U.S. Senate delegation led by the leader of the Republican minority in the upper house of Congress Mitchell McConnell is a strong signal of bipartisan support for Ukraine from the United States Congress and the American people," Zelenskyy said on Telegram.

Zelenskyy added: "Thank you for your leadership in helping us fight not only for our country, but also for democratic values and freedoms. We really appreciate it.”

-ABC News' Clack Bentson

Russian military commander Vadim Shishimarin, accused of killing a Ukrainian civilian in the Sumy region on Feb. 28, is set to go to trial on May 19, according to Ukraine's prosecutor general Iryna Venediktova.

The 21-year-old soldier allegedly fired his AK-47 at a car driven by a 62-year-old Ukrainian man, killing him at the scene, Venediktova said.

Shishmarin is charged with murder and two counts of robbery.

Prosecutor Andriy Syniuk said Shishmarin has cooperated throughout the investigation.

He is the first member of the Russian military to face charges, Venediktova said.

He could face a life sentence if convicted.

-ABC News' Nadine El-Bawab and Tatiana Rymarenko

On a Friday phone call with Swedish Prime Minister Magdalena Andersson and Finnish President Sauli Niinistö, President Joe Biden "underscored his support for NATO’s Open Door policy and for the right of Finland and Sweden to decide their own future, foreign policy, and security arrangements," according to the White House.

White House press secretary Jen Psaki said Thursday that the U.S. "would support" Finland and Sweden applying to join NATO "should they choose to apply."

Dmitry Polyanskiy, Russian deputy ambassador to the United Nations, told a British news podcast that Finland and Sweden officials "know the moment they become members of the NATO, it will imply certain mirror moves on the Russian side. … If there are NATO detachments in those territories, these territories would become a target -- or a possible target -- for a strike."

On Friday's call, Biden, Andersson and Niinistö "reiterated their shared commitment to continued coordination in support of Ukraine and the Ukrainian people affected by the war," according to the White House statement.

-ABC News' Molly Nagle