Shelling is ongoing near the largest nuclear power plant in Europe.
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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Twenty-one people were killed and another 22 were injured in a Russian missile strike on a train station in Chaplyne, in the central Ukraine region of Dnipropetrovsk, said Kyrylo Tymoshenko, deputy head of the president's office.
-ABC News' Christine Theodorou and Max Uzol
The White House said the U.S. believes Russia could hold "sham referenda" in occupied Ukrainian territory within days or weeks.
White House spokesman John Kirby said last month that Russia was "installing illegitimate proxy officials in the areas of Ukraine that are under its control" who would then arrange "sham referenda" as a precursor to annexation.
Kirby told reporters Wednesday that the U.S. government believes "these referenda could begin in a matter of days or weeks."
"We have information that Russia continues to prepare to hold these sham referenda in Kherson, Zaporizhzhia, the so-called Donetsk and Luhansk People's Republics," Kirby said. "We've also learned that Russian leadership has instructed officials to begin preparing to hold these sham referenda, particularly in Kharkiv, as well."
"We expect Russia to try to manipulate the results of these referenda to falsely claim that the Ukrainian people want to join Russia," he continued. "It will be critical to call out and counter this disinformation in real time."
"Any claim that the Ukrainian people somehow want to join Russia is simply not true," Kirby said, citing polling data. It's clear, he added, that Ukrainians "value and treasure their independence."
President Joe Biden and Ukrainian President Volodymyr Zelenskyy will speak on the phone on Thursday, Kirby said.
-ABC News’ Ben Gittleson
Queen Elizabeth released a statement Wednesday marking Ukrainian Independence Day.
"It gives me great pleasure to send Your Excellency and the people of Ukraine my warmest greetings on the celebration of your Independence Day," she said. "In this most challenging year, I hope that today will be a time for the Ukrainian people, both in Ukraine and around the world, to celebrate their culture, history and identity. May we look to better times in the future."
President Joe Biden in a statement Wednesday said he was "proud to announce our biggest tranche of security assistance to date" to Ukraine: "approximately $2.98 billion of weapons and equipment."
"This will allow Ukraine to acquire air defense systems, artillery systems and munitions, counter-unmanned aerial systems, and radars to ensure it can continue to defend itself over the long term," Biden said.
Biden confirmed the money would come through the Ukraine Security Assistance Initiative. The USAI money can be spent on contracts with the defense industry to produce new equipment for Ukraine.
Biden in his statement also marked Ukrainian Independence Day, saying, "Ukrainians have inspired the world with their extraordinary courage and dedication to freedom."
"Today is not only a celebration of the past but a resounding affirmation that Ukraine proudly remains -- and will remain -- a sovereign and independent nation," he said.
He continued, "I know this Independence Day is bittersweet for many Ukrainians as thousands have been killed or wounded, millions have been displaced from their homes, and so many others have fallen victim to Russian atrocities and attacks."
"Today and every day, we stand with the Ukrainian people to proclaim that the darkness that drives autocracy is no match for the flame of liberty that lights the souls of free people everywhere," Biden said.
-ABC News' Ben Gittleson
