Russian shelling in eastern Ukraine's Kharkiv Oblast over the past 24 hours left four civilians dead, the regional governor said Wednesday.

A woman was killed in the village of Zolochev, while a 12-year-old boy died in the village of Ivanivka, northwest of Kharkiv city. Two more people were killed in the village of Shestakove, northeast of Kharkiv city. Seven other civilians were injured in the region, according to Kharkiv Oblast Gov. Oleg Synegubov.

"The enemy is acting insidiously, striking at civilians and civilian infrastructure," Synegubov said in a statement via Telegram. "But he will answer for all his crimes! Ukraine will win!"

Over half of Sieverodonetsk is now likely occupied by Russian forces, including Chechen fighters, the U.K. Ministry of Defense said Wednesday in an intelligence update.

The ministry said fighting intensified in the streets of the key eastern Ukrainian city on Monday and Tuesday, "with Russian forces pushing closer to the town centre." Sieverodonetsk is located in the war-torn Luhansk Oblast of eastern Ukraine's disputed Donbas region.

"Russian ground operations remain tightly focused, with the weight of fire power concentrated within a small sector of Luhansk Oblast," the ministry said.

"Beyond the Donbas, Russia continues to conduct long-range missile strikes against infrastructure across Ukraine," the ministry added. "The strategically important bridge links Ukraine with Romania and with Ukraine's ports on the Danube, which have become critical to Ukrainian exports after the blockade of Ukrainian Black Sea ports by Russia."

The U.S. will provide Ukraine with "more advanced rocket systems and munitions," President Joe Biden confirmed in a New York Times op-ed published Tuesday.

The systems "will enable them to more precisely strike key targets on the battlefield in Ukraine," he wrote.

Russian Foreign Minister Sergei Lavrov warned last week that providing more advanced rockets would be a new "unacceptable escalation" because they could hypothetically be used to strike within Russian territory.

But Biden told reporters Monday that the U.S. will not "send to Ukraine rocket systems that can strike into Russia," and he and the administration are making efforts to emphasize that these new rocket systems will be used by the Ukrainians on the battlefield in their own country.

-ABC News' Conor Finnegan

Russia's invasion of Ukraine has left 5.2 million kids in need of humanitarian help, according to UNICEF.

At least 262 children have been killed and another 415 have been hurt since Feb. 24, UNICEF said.

Nearly two-thirds have been displaced, UNICEF said.

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