Russia's invasion of Ukraine has already engaged around 330,000 Russian personnel, Brigadier General Oleksiy Hromo of the General Staff of the Ukrainian Armed Forces told local media on Thursday.

“[Russian] groups at various axes are close to 150,000 strong. If we add their air and sea components, there are about 220,000 military personnel,” Hromo said. Russia also deployed “units of the national army combat reserve, the federal service of guard forces, and mobilization units,” the Brigadier General added.

Hromo's sobering account came on the back of claims made by a top Ukrainian official earlier on Wednesday that revealed mounting Ukrainian casualties. Up to 1,000 Ukrainian soldiers are being killed or wounded each day in the Donbas region of eastern Ukraine, with 200 to 500 killed on average and many more wounded, said David Arakhamia, who heads the presidential faction in the Ukrainian parliament.

In early June, Ukrainian President Volodymyr Zelenskyy said daily fatalities among Ukrainian ranks at the Donbas front were between 60 to 100 troops.

Arakhamia, one of Zelenskyy's closest advisers who oversees Ukraine's stalled negotiations with Russia, has been leading a Ukrainian delegation in Washington this week in a bid to lobby the Biden administration and Congress.

Arakhamia's team want to see the pace of weapons shipments increased and is pushing for a designation of Russia as a state sponsor of terrorism.

-ABC News' Edward Szekeres, Yuriy Zaliznyak, Yulia Drozd and Max Uzol

The United Kingdom announced a new wave of sanctions on Thursday targeting Russians involved in the barbaric treatment of children in Ukraine.

Maria Lvova-Belova, Russia's Children Rights Commissioner, tops the new list of sanctioned individuals for her alleged involvement in the forced transfer and adoption of Ukrainian children. She has been accused of enabling 2,000 vulnerable children being violently taken from the Luhansk and Donetsk regions and orchestrating a new policy to facilitate their forced adoptions in Russia.

“Today we are targeting the enablers and perpetrators of [Russian President Vladimir] Putin’s war who have brought untold suffering to Ukraine, including the forced transfer and adoption of children,” U.K. Foreign Secretary Liz Truss said in a press release.

More than 900 children were injured in Ukraine as a result of the full-scale armed aggression by the Russian Federation, according to the Ukrainian Prosecutor General’s latest report. Over 320 children were killed and more than 580 were injured.

These figures are far from being final, with more information slowly trickling in from places of active hostilities, as well as the temporarily occupied and liberated territories.

The UK's sanction list also includes Patriarch Kirill, the head of the Russian Orthodox Church, for his support and endorsement of Putin’s war.

Several members of Putin's political elite, along with four Military Colonels from a unit known to have killed, raped and tortured civilians in the Ukrainian town of Bucha, appear on the list too.

“Putin’s allies continue to choose to turn a blind eye to alleged war crimes and support his bloody offensive,” the U.K. government said. With Putin’s aggression reaching beyond Ukraine as Russian exports fuel conflict across the globe, the official press release read, the new sanctions also hit Myanmar’s military Junta.

The Junta relies heavily on Russian air assets and limiting it will cut Putin off from profiting from sales that fund his war machine, the U.K. said.

-ABC News' Edward Szekeres, Yuriy Zaliznyak, Yulia Drozd and Max Uzol

The State Department has still not confirmed reports that two former U.S. service members who volunteered to help Ukrainian forces have gone missing, spokesperson Ned Price said Thursday.

The Americans, Andy Tai Ngoc Huynh and Alexander Drueke, are both from Alabama.

"We are limited in terms of what we know at the moment," Price said. "We're closely monitoring the situation we are in contact with Ukrainian authorities, as well as with the International Committee of the Red Cross, and the families of the two reported missing U.S. citizens."

The department has not "seen anything from the Russians indicating that two such individuals are in their custody," Price said.

"If the Russians were to claim that they had such individuals, I assume we would pursue that. If we had reason to believe -- credible reasons to believe -- that these individuals were in Russian custody, we would pursue that as appropriate," Price continued.

Price was asked whether the department was tracking any other cases of Americans purportedly captured on the battlefield, and he said the department was aware of reports about "one additional American whose whereabouts are unknown.”

"Similarly, our understanding was that this individual had traveled to Ukraine to take up arms," Price said. He said the person was identified as missing "in recent weeks" and that the State Department was also in contact with their family.

Alabama Rep. Terri Sewell said that Drueke’s mother reached out to her office after losing contact with him. Sewell is helping the family locate him. Alabama Rep. Robert Aderholt said his office is helping in the search for Huynh after his family reached out to the congressman's office this week.

-ABC News' Shannon Crawford

In the first visit of EU leaders to the Ukrainian capital since Russia’s invasion, German Chancellor Olaf Scholz, French President Emmanuel Macron, Italian Prime Minister Mario Draghi and Romanian President Klaus Iohannis made clear their message of support and solidarity.

Scholz said, "My colleagues and I came here to Kyiv today with a clear message: Ukraine belongs to the European family."

Macron added, "All four of us support [Ukraine's] immediate EU candidacy."

The leaders discussed the possibility of further sanctions against Russia as well as how to rebuild Ukraine after the war.

Earlier in the day, the EU leaders toured Irpin, a town northeast of Kyiv, which was hit by heavy Russian artillery early in the war.

-ABC News' Britt Clennett and Ibtissem Guenfoud

Russia claimed Wednesday that its military has taken complete control of Mariupol, a strategic port city in Ukraine's war-torn east.

"Peaceful life is being established in the territories of the LPR and DPR and Ukraine liberated from nationalists, including Mariupol, the largest industrial and transport hub on the Sea of ​​Azov," Russian Defense Minister Sergei Shoigu said during a teleconference. "It is under the control of the Russian army."

According to Shoigu, Russian forces have "securely blocked" remaining Ukrainian fighters on the grounds of the Azovstal Iron and Steel Works plant in Mariupol. The sprawling industrial site, which includes a maze of underground tunnels and bunkers, is the last pocket of Ukrainian resistance in Mariupol.

"In accordance with the instructions of the supreme commander, the remnants of the militants located in the industrial zone of the Azovstal plant are securely blocked around the entire perimeter of this territory," Shoigu told reporters. "Repeated proposals to the nationalists to release civilians and lay down their arms with a guarantee of saving lives and decent treatment in accordance with international law, they have ignored. We continue these attempts."

During a daily briefing call later Wednesday, Kremlin spokesman Dmitry Peskov said the situation at the blockaded plant hadn't changed and denied reports that Russian forces had begun storming the bombed-out territory, but said they have seen sporadic attempts by Ukrainian fighters to open fire.

"The supreme commander-in-chief has publicly ordered that the storm be canceled. There is no storm," Peksov told reporters. "We can see that escalations happen as the fighters come to firing positions. These attempts are suppressed quite rapidly."

ABC News recently spoke with Denys Prokopenko, a commander of the Azov Regiment, a far-right group now part of the Ukrainian military that was among the units defending Mariupol and is holed up inside the Azovstal plant with others. He said the fighters inside have tried to initiate a cease-fire to create conditions to allow people to flee but have yet to surrender, despite the odds. There are a number of people wounded and dead inside the plant, with some out of reach after sections of a bunker collapsed from Russian bombardment, according to Prokopenko.

"We are in full blockade, full circle of surrounding and we are under fire and the city is under fire," Prokopenko told ABC News.

Earlier this week, a humanitarian convoy evacuated more than 100 civilians from the Azovstal plant and escorted them safely to Zaporizhzhia, a Ukrainian government-controlled city located about 140 miles northwest of Mariupol. Hundreds more civilians remain trapped inside the plant and Russian forces have resumed shelling of the area, according to Ukrainian officials.

-ABC News' Clark Bentson, Dragana Jovanovic and Ian Pannell