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.
An advisor to Ukrainian President Volodymyr Zelenskyy said that U.S. Secretary of State Antony Blinken and U.S. Defense Chief Lloyd Austin are meeting with Ukraine's leader on Sunday in Kyiv.
The adviser, Oleksii Arestovich, said in an interview on Ukrainian TV late Sunday that the talks are going on "right now."
-ABC News' Jason Volack
More than 2.9 million people have fled Ukraine and sought refuge in Poland since the Russian invasion began in February, the Polish Border Guard said on Sunday.
In recent days, however, the number of people crossing the border into Poland has fallen, while the number of refugees going back into Ukraine has risen, according to the border guard.
On Saturday, about 21,100 people entered Ukraine from Poland, while 15,100 fled to Poland from Ukraine, the agency said on Twitter.
Ukraine's losses, including destroyed homes and massive damage to the country's infrastructure, has topped $1 trillion since Russian forces invaded the country two months ago, according to Ukraine's top economic advisor.
Oleg Ustenko, economic adviser the Ukrainian president, announced the country's staggering losses in a televised address on Sunday.
"This is what was destroyed by the Russian invaders in our assets. It is clear that this figure literally increased every day ... the aggressor destroyed our infrastructure, destroyed the homes of our citizens, destroyed everything that could be destroyed by their own and air strikes, and simply by dropping bombs and everything they did," Ustenko said.
Ustenko said additional losses have come as a result of Ukraine's declining gross domestic product.
"It is this figure that we must focus on," Ustenko said. "It is this figure that should be compensated by the Russian Federation immediately after our victory."
The opening of humanitarian corridors for people to escape the besieged Ukrainian port city of Mariupol did not occur as scheduled on Sunday because Russian troops in the area did not confirm a cease-fire, according to Ukrainian Deputy Prime Minister Iryna Vereshchuk.
Vereshchuk called on the United Nations to step in and provide the escape routes for civilians still trapped in Mariupol by the fighting.
She said the problem over establishing humanitarian corridors out of Mariupol should be raised with U.N. Secretary-General Antonio Guterres.
