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

One person has been killed and six others are injured from shelling in the Solokhi village in Belgorod, Russia, according to Belgorod Gov. Vyacheslav Gladkov. A 14-year-old boy is among the injured, the governor said.

This area is less than 7 miles from the Russia-Ukraine border.

Gladkov said the shelling originated from Ukraine's side of the border and that this was the most serious incident since Ukrainian forces began firing on the region. Ukrainian authorities have not confirmed that Ukrainian forces are firing on Russia's side of the border.

As Sweden and Finland consider NATO memberships, British Prime Minister Boris Johnson signed new security pacts with the leaders of both nations on Wednesday, ensuring the U.K. could give military support even if the countries are not NATO members.

Johnson said the invasion of Ukraine "sadly" opened a new chapter.

"Our armed forces will train, operate and exercise together -- marrying our defense and security capabilities and formalizing a pledge that we will always come to one another’s aid," he said at a news conference.

-ABC News' Christine Theodorou

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.