Russia-Ukraine updates: US sanctions Russian military shipbuilder, diamond miner

The International Committee of the Red Cross is calling for an urgent solution for the "life-and-death" situation facing the hundreds of thousands of civilians trapped in Mariupol without access to running water and electricity as the heavy airstrikes from Russian forces continue.

A "worst-case" scenario awaits those who remain in the city unless a humanitarian agreement among the fighting parties is reached immediately, the ICRC said in a press release on Sunday.

"We call on all parties involved in the fighting to place humanitarian imperatives first. People in Mariupol have endured a weekslong life-and-death nightmare. This needs to stop now," Peter Maurer, president of the ICRC, said in a statement. "Their safety and their access to food, water and shelter must be guaranteed."

People of all ages, including Red Cross staff, are sheltering in unheated basements and risking their lives to make short runs outside for food and water, according to the ICRC.

Dead bodies, both of civilians and combatants, remain trapped under the rubble or lying in the open where they fell, and those suffering injuries or chronic, debilitating conditions are unable to seek treatment.

"The sound of warfare is constant. Buildings are struck, and shrapnel flies everywhere," said ICRC's operational leader in Mariupol, Sasha Volkov. "This is the situation every person in the city faces."

-ABC News' Zoe Magee

An American who traveled to Ukraine to assist in the country's stand against the Russian invasion described the heavy bombardment parts of western Ukraine are now seeing.

Glock Dara, 29, was asleep at the military training ground in Yavoric, on the outskirts of Lviv, when he heard the first missiles begin to strike on Sunday morning.

"I didn’t have time to panic. I just focused on running as fast as I can," Dara told ABC News. "Hella chaos, bombs falling left and right -- you’re just praying to God it doesn’t happen to you."

The strikes left at least 35 dead and 134 wounded, according to Ukrainian officials. Russian officials claim 180 foreign mercenaries are dead.

Dara is one of roughly two dozen soldiers evacuated from Yavoriv and brought to the Korczowa refugee center in Poland Sunday afternoon, about 15 miles away.

All of the men ABC News spoke with at the refugee center were volunteer foreign fighters from Ireland, France, Boston -- most dressed in uniforms bearing the Ukrainian flag. The base served as a launching pad for foreign fighters who were trained there and then deployed across the country, one medic from Ireland told ABC News.

"A lot" of Americans are at the American base as well, Dara said. He and some of the men he travelled with are now planning to re-group in Krakow, but Dara already intends to back to Lviv, he said.

"I came here as a volunteer counter-terrorist," he added.

The Korczowa refugee center has already seen a significant increase in the number of people coming in from western Ukraine in just the last couple days, volunteers at the shelter told ABC News.

-ABC News' Ines De La Cuerta

Ukraine Energy Minister Herman Galushchenko confirmed Sunday that power lines have been repaired to the Chernobyl Nuclear Power Plant in northern Ukraine, which was seized by Russian forces during a fierce battle last week.

"Our Ukrainian energy companies, risking their own health and lives, were able to avert the risk of a possible nuclear catastrophe that threatened the whole of Europe," Galushchenko said in a statement.

He said the restoration of electricity to the plant will enable its cooling systems of nuclear waste assemblies to work normally again, not from backup power.

In 1986, reactor No. 4 at the power plant, about 65 miles north of the capital Kyiv, exploded, spewing enormous amounts of radioactive material into the atmosphere and causing more than 100,000 people in a 1,000-square-mile radius to evacuate.

Nuclear experts and Ukrainian government officials had expressed concern about potential health hazards from radioactive material spreading from the defunct plant amid the fighting.

British officials are exploring whether they can use the homes of sanctioned Russian oligarchs to house refugees from the war in Ukraine, a top United Kingdom minister told the BBC.

Michael Gove, the British secretary of state for housing, said he wants to explore options for using oligarchs' homes in Great Britain to shelter the millions of refugees fleeing Ukraine "for as long as they are sanctioned."

“There’s quite a high legal bar to cross and we’re not talking about permanent confiscation. But we are saying, ‘You’re sanctioned, you’re supporting Putin, this home is here, you have no right to use or profit from it," Grove said. "If we can use it in order to help others, let’s do that."