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

Secretary of Defense Lloyd Austin spoke to his Russian counterpart, Sergei Shoigu, for the first time since the invasion of Ukraine began, according to a statement from Pentagon press secretary John Kirby.

Austin urged for an immediate ceasefire and "emphasized the importance of maintaining lines of communication," the statement said.

-ABC News' Matt Seyler

Russian troops suffered "significant" loss while attempting to cross a river in the disputed Donbas region of war-torn eastern Ukraine, the U.K. Ministry of Defense said Friday in an intelligence update.

"Ukrainian forces successfully prevented an attempted Russian river crossing in the Donbas," the ministry said. "Images indicate that during the crossing of the Siverskyi Donets river west of Severodonetsk, Russia lost significant armoured manoeuvre elements of at least one Battalion Tactical Group as well as the deployed pontoon bridging equipment."

"Conducting river crossings in a contested environment is a highly risky manoeuvre and speaks to the pressure the Russian commanders are under to make progress in their operations in eastern Ukraine," the ministry added. "Russian forces have failed to make any significant advances despite concentrating forces in this area after withdrawing and redeploying units from the Kyiv and Chernihiv Oblasts."

On Wednesday, the Ukrainian Ministry of Defense released images purportedly showing a wrecked pontoon crossing over the Siverskyi Donets river, with a number of damaged or destroyed armored vehicles on both banks.

"Artillerymen of the 17th tank brigade of the #UAarmy have opened the holiday season for [Russian forces]," the ministry said in a post on Twitter, alongside the photos. "Some bathed in the Siverskyi Donets River, and some were burned by the May sun."

The Ukrainian Armed Forces' Strategic Communications Directorate also tweeted images of the scene, purportedly showing the smoking wreckage after artillery units and land forces "destroyed all attempts by the Russian occupiers to cross the Seversky Donets River."

Mariupol has not yet fallen, despite Russia's demands that Ukrainian troops defending the besieged Ukrainian port city surrender, according to Ukrainian Prime Minister Denys Shmyhal.

"There [are] still our military forces, our soldiers, so they will fight until the end," Shmyhal told ABC News' George Stephanopoulos in an exclusive interview Sunday on "This Week."

Mariupol is a strategic city for Moscow because it would allow Russian forces in the south to connect with troops in eastern Ukraine's contested Donbas region. It would also give Moscow a key port.

Although Mariupol remains under the Ukrainian government's control, Shmyhal said the city's residents are suffering.

"They have no water, no food, no heat, no electricity," he said. "They ask all of our partners to support and help stop this humanitarian catastrophe."

-ABC News' Monica Dunn