Ukrainian President Volodymyr Zelenskyy warned of continued devastation on par with what has been seen in Mariupol and Volnovakha amid heavy fighting in the eastern part of the country.

"Russia wants to destroy every city in Donbas, 'every' is not an exaggeration," he said in his latest national address.

"This is probably the fastest example of the complete degradation of any state -- the path that the Russian state has covered in 107 days," the president continued.

In recent days, Russian forces have encircled Severodonetsk, the largest city still held by Ukrainian troops in contested Donbas. Zelenskky has said the battle there could determine the fate of eastern Ukraine.

"The Ukrainian troops are doing everything to stop the offensive of the occupiers. As much as possible. As much as the heavy weapons, modern artillery -- all that we have asked and continue to ask our partners for -- allow them to," the president said Friday.

Up to 100 Ukrainian soldiers are killed and another 500 are injured each day, according to Ukrainian Defense Minister Oleksiy Reznikov.

Reznikov said in a Facebook post Thursday that Russia has "many more means in store to devour human lives in a bid to satisfy its imperial ego."

"That is why we emphasize: Ukraine desperately needs heavy weapons, and very fast," Reznikov said.

Among the weapons he's requesting are "fighter jets, anti-aircraft and missile defence systems to protect our skies."

-ABC News' Will Gretsky

At least 4.8 million Ukrainian refugees are now scattered across 44 countries in Europe, according to the United Nations High Commissioner for Refugees.

The UNHCR has recorded 7.3 million border crossings from Ukraine and another 2.3 million crossings back into the country.

"Although the security situation in Ukraine remains fragile, crossings back and forth have been recorded," the agency said in a statement. "Some cross to Ukraine to assess the situation, check property, visit family members or help them to leave. Others are going to Western Ukraine and areas around Kyiv and Chernihiv intending to stay. Many who have moved back have found their homes severely damaged and struggled to find jobs -- as the war continues to have a devastating economic impact -- and had no choice but to leave again."

-ABC News' Will Gretsky

The fight for the eastern Ukrainian city of Severodonetsk will determine the fate of the wider Donbas region, according to Ukrainian President Volodymyr Zelenskyy.

"Severodonetsk remains the epicenter of the confrontation in Donbas. We defend our positions, inflict significant losses on the enemy," Zelenskyy said late Wednesday in his nightly address. "This is a very fierce battle, very difficult. Probably one of the most difficult throughout this war. I am grateful to everyone who defends this direction. In many ways, the fate of our Donbas is being decided there."

After launching an invasion of neighboring Ukraine on Feb. 24, Russian forces failed to take control of the capital, Kyiv, and other major government centers as they faced tough resistance from Ukrainian troops. Russian forces then switched attention to Donbas, which comprises the self-proclaimed republics controlled by Moscow-backed separatists in eastern Ukraine's Luhansk and Donetsk oblasts.

Severodonetsk, an industrial hub, is the largest city still held by Ukrainian troops in contested Donbas. In recent days, Russian forces have encircled the city as they advanced in the region, creating a pocket that could trap Ukrainian defenders there and in the neighboring city of Lysychansk.

Severodonetsk and Lysychansk are the last major cities in the Luhansk area still controlled by Ukraine. Last week, the U.K. Ministry of Defense said in an intelligence update that Russian forces had seized most of Severodonetsk, but that the main road into the pocket likely remained under Ukrainian control.

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