The Ukrainian prosecutor’s office has brought its first indictment against a Russian soldier for allegedly shooting and killing a Ukrainian civilian.

Vadim Shishimarinov, a 21-year-old soldier in Russia's 4th Armored Division, allegedly fired his AK-47 at a car driven by a 62-year-old Ukrainian man, killing him at the scene, Ukraine's prosecutor general Iryna Venediktova said.

He could face a life sentence if convicted of the shooting, which unfolded on Feb. 28 in the village of Chupakhivka.

-ABC News' Tomek Rolski

Fighting has continued on Ukraine's Zmiinyi Island, also known as Snake Island, "with Russia repeatedly trying to reinforce its exposed garrison located there," the U.K. Ministry of Defense said Wednesday in an intelligence update.

"If Russia consolidates its position on Zmiinyi Island with strategic air defence and coastal defence cruise missiles, they could dominate the north-western Black Sea," the ministry warned.

The island is strategically located, as it provides access to Ukraine's major port cities, including Odesa, the country's largest seaport and one of the largest in the Black Sea basin, serving as a major gateway for grain shipments and other key exports.

Ukraine, however, has managed to successfully strike Russian air defenses and resupply vessels with drones, according to the ministry.

"Russia's resupply vessels have minimum protection in the western Black Sea, following the Russian Navy’s retreat to Crimea after the loss of the Moskva," the ministry added.

Ukrainian President Volodymyr Zelenskyy on Wednesday thanked the U.S. House of Representatives for its approval of a nearly $40 billion package of humanitarian and military aid to Ukraine in a bill passed on Tuesday.

“We are looking forward to the consideration of this important document for us by the Senate,” Zelenskyy wrote in a tweet expressing gratitude to House Speaker Nancy Pelosi, President Joe Biden and “all friends of Ukraine” in the House.

Earlier on Tuesday, two senators unveiled a resolution calling on the Biden administration to designate Russia as a state sponsor of terrorism. Sen. Richard Blumenthal, D.-Conn., and Sen. Lindsey Graham, R.-S.C., said the designation, which could result in further sanctions for Russia, is warranted by Russia's war on Ukraine and conduct elsewhere under President Vladimir Putin.

“Putin is a thug, and a bully, and he will continue being an increasing threat to Europe and the world unless he is stopped,” Blumenthal said at a press conference, adding, “If there's anybody who embodies terrorism, totalitarianism and tyranny, it's Putin.”

The resolution was originally requested by the Ukrainian parliament, but Secretary of State Antony Blinken has so far declined to add Russia to the list of countries -- Cuba, Iran, North Korea and Syria -- considered to be state sponsors.

Russia's Ministry of Health sent the World Health Organization a letter in which it "strongly rejects" its responsibility for the rising death toll in Ukraine.

“The health emergency in Ukraine and neighboring countries is caused by the unconstitutional coup that took place in this country in 2014, and by the subsequent military aggression of the Kyiv regime against the population of Donbass in the period of 2014–2022,” Andrey Plutnitsky, Russia's envoy to the WHO, wrote in the letter.

Plutnitsky called on WHO member states to pay “special attention” to “the military biological activities undertaken by a number of countries on the territory of Ukraine, which represent a significant danger to the region.”

Members of the Russian military are trying to hide their involvement in some hostilities in Ukraine, the Ukrainian Defense Ministry's intelligence service said on Wednesday.

Russian troops, including some from the air and space forces, have demanded that the command keep their involvement in the invasion secret in order to avoid further possible responsibility for war crimes, the Ukrainian intelligence claimed.

Meanwhile, the U.S. Department of Defense confirmed that 89 of the 90 M777 Howitzers promised to Ukraine have been handed over to the Ukrainian military.

Of the total count of 184,000 rounds of ammunition committed to Ukraine, “65 percent, so almost 120,000 rounds, are in [Ukraine],” a senior defense official said at a background briefing on Tuesday. The Russians added two battalion tactical groups to their force in Ukraine in the past 24 hours, the official added, bringing the new count of operational Russian BGTs up to 99.

-ABC News' Edward Szekeres, Max Uzol, Yuriy Zaliznyak and Irene Hnatiuk

The House on Tuesday approved a nearly $40 billion package of humanitarian and military aid to Ukraine, the latest tranche of relief to the country the U.S. is aggressively backing in its fight against Russia.

The bill, which was finalized earlier Tuesday and includes nearly $7 billion more funding than requested by the Biden administration, was approved in a 368-57 vote, with all Democrats backing the bill and all opposition coming from Republicans.

With the vote, Congress has now directed more than $50 billion to support Ukraine in the war with Russia. The House voted 36-169 on March 9 on a $13.6 billion package for Ukraine and other key European allies.

The Senate is expected to vote on the measure in the coming days.

The package includes $6 billion to help train, equip and support the Ukrainian armed forces, and more than $9 billion to replenish the U.S. stockpiles of military equipment and ammunition in the U.S. and abroad that have been tapped to re-arm Ukraine.

The measure would also help fund and support U.S. troops stationed in Europe and the operation of a Patriot air defense missile system in Europe, and it includes more than $900 million to support Ukranian refugees with housing, counseling and English language classes, as well as helping process and screen those traveling to the United States.

Additionally, the bill directs the inspector general of the Defense Department to provide a written report to the House and Senate defense committees reviewing the Ukraine program spending within 120 days of the law's enactment.

-ABC News' Ben Siegel

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