The Americans, Andy Tai Ngoc Huynh and Alexander Drueke, are both from Alabama.
Russian President Vladimir Putin's "special military operation" into neighboring Ukraine began on Feb. 24, with Russian forces invading from Belarus, to the north, and Russia, to the east. Ukrainian troops have offered "stiff resistance," according to U.S. officials.
The Russian military has since launched a full-scale ground offensive in eastern Ukraine's disputed Donbas region, capturing the strategic port city of Mariupol and securing a coastal corridor to the Moscow-annexed Crimean Peninsula.
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A look at the two leaders at the center of the war in Ukraine and how they both rose to power, the difference in their leadership and what led to this moment in history.
Vadym Boychenko, the mayor of the hard-hit Ukrainian city of Mariupol, told The Associated Press that more than 10,000 residents have been killed.
Boychenko said, with corpses "carpeted through the streets," it's possible that the southeastern city's death toll is over 20,000.
-ABC News' Mike Trew
The Ukrainian Armed Forces said Monday that Russian troops are continuing to attack hard-hit Mariupol in southeastern Ukraine.
The Ukrainians said the Russians are still partially blocking the northeast city of Kharkiv using rockets, artillery and mortars.
In Kherson, in the south of Ukraine, Russian forces are trying to gain a foothold in the administrative borders, according to the Ukrainians.
And in Severodonetsk in eastern Ukraine, Russian forces made an unsuccessful attempt to storm the city and weren't able to advance deeper into Ukraine's territory, the Ukrainians said.
-ABC News' Irene Hnatiu
More than 4.5 million people have been forced to flee Ukraine since Russian forces invaded on Feb. 24, according to the latest figures from the United Nations Refugee Agency.
The tally from the U.N. High Commissioner for Refugees (UNHCR) amounts to just over 10% of Ukraine's population -- which the World Bank counted at 44 million at the end of 2020 -- on the move across borders in 47 days.
More than half of the refugees crossed into neighboring Poland, UNHCR figures show.
"The escalation of conflict in Ukraine has caused civilian casualties and destruction of civilian infrastructure, forcing people to flee their homes seeking safety, protection and assistance," the UNHCR said in a statement alongside the data updated Sunday.
"In the first five weeks, more than four million refugees from Ukraine crossed borders into neighbouring countries, and many more have been forced to move inside the country," the agency noted. "In light of the emergency and the scale of humanitarian needs of refugees from Ukraine, an inter-agency regional refugee response is being carried out, in support of the efforts of refugee-hosting countries."
Russia's invasion is expected to shrink Ukraine's economy by about 45.1% this year, the World Bank said on Monday.
"Ukraine needs massive financial support immediately," said Anna Bjerde, World Bank vice president for the Europe and Central Asia region.
The World Bank said a $3 billion package is being prepared for Ukraine. Already $925 million in emergency funding has been mobilized for Ukraine to help pay wages for hospital workers, pensions for the elderly and social programs for the vulnerable. The Bank Group is also looking at how to support refugees in host countries.
Meanwhile, Russia, hit by unprecedented sanctions, has already plunged into a deep recession with output projected to contract by 11.2% in 2022, the World Bank said.
-ABC News' Christine Theodorou
