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

About 1.4 million people have been left without clean running water in war-torn eastern Ukraine and an estimated 4.6 million people across the country are at risk of losing their supply, the United Nations Children's Fund reported Wednesday.

UNICEF officials said heavy fighting in eastern Ukraine, including the widespread use of explosive weapons in populated areas, has decimated a large part of the region's water systems. The agency tallied 20 separate incidents in which water infrastructure has been damaged or destroyed and warned of a "risk of complete collapse."

Damaged electrical grids have shut down water pumps and explosion-related damage to pipelines are disrupting the flow of water, according to UNICEF.

"Water is essential for life and a right for everyone," Osnat Lubrani, the U.N. resident coordinator in Ukraine, said in a statement. "The health risks, particularly for children and the elderly, caused by water stoppages are severe, as people are forced to use dirty water sources, resulting in diarrhoea and other deadly infectious diseases."

Murat Sahin, a UNICEF Ukraine representative, added that, “Young children who live in conflict zones are 20 times more likely to die from diarrheal diseases linked to unsafe water than from direct violence, as a result of war."

In hard-hit Mariupol, which has been under siege since the start of the Russian invasion on Feb. 24, thousands of residents trapped in the city are seeking any water they can find and resorting to dirty water sources, according to UNICEF. Major cities across the Donetsk and Luhansk regions are also cut off from water supplies.

The water systems in Sumy, Chernihiv and Kharkiv have also been seriously damaged, UNICEF said. An additional 340,000 people are at risk of losing their water supply from a reservoir in Horlivka in the Donetsk region that is inching closer to running dry, according to UNICEF.

Agency officials said that prior to the invasion, much of the water systems in eastern Ukraine were already ailing after eight years of a low-grade conflict in the region.

-ABC News' Christine Theodorou

Russia claimed Wednesday that more than a thousand Ukrainian soldiers had surrendered in Mariupol, a besieged port city in southeastern Ukraine that is still held by Ukrainian forces.

"In Mariupol city, near the 'Illich' Steelworks, 1,026 Ukrainian servicemen of the 36th Marine Brigade have voluntarily laid down their arms and surrendered as a result of a successful offensive by the Russian Armed Forces and Donetsk People's Republic militia units," the Russian Ministry of Defense said in a statement.

The surrendering troops included 162 officers and 47 women, according to the ministry.

"151 wounded Ukrainian servicemen of the 36th Marine Brigade received primary medical care immediately on the spot, after that they were all taken to the Mariupol city hospital for further treatment," the ministry added.

The Biden administration could announce as early as Wednesday upward of $750 million in additional military assistance to Ukraine, a U.S. official told ABC News.

The new assistance could possibly include a range of military hardware -- including howitzers, artillery and Humvees -- though the full package still needs to be finalized, the official said.

-ABC News' Luis Martinez

Correction: Mi-17 helicopters are not being considered as part of the package, as previously reported.

President Joe Biden used the word "genocide" for the first time to describe Russia's actions in Ukraine during remarks on Tuesday.

"Your family budget, your ability to fill up your tank -- none of it should on hinge on whether a dictator declares war and commits genocide half a world away," Biden said in Menlo, Iowa, during remarks primarily about the U.S. economy.

Biden was asked by reporters on April 4 if he thought the atrocities in Bucha were a genocide, as Ukrainian President Volodymyr Zelenskyy had claimed. "No, I think it is a war crime," Biden responded then.

That same day, Biden's national security adviser, Jake Sullivan, said the administration had not yet seen the "systematic deprivation of life" necessary to meet the definition of genocide.

Biden confirmed his word choice to the White House pool Tuesday evening before boarding Air Force One, saying that since last week the "evidence is mounting."

"Yes, I called it genocide," Biden said. "Because it has become clearer and clearer that Putin is just trying to wipe out the idea of even being able to be a Ukrainian."

He then qualified that the determination of genocide is officially up to legal experts, but that "it sure seems that way to me."

-ABC News' Sarah Kolinovsky