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.
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.
Here's how the news is developing. All times Eastern.
Apr 10, 2022, 5:00 PM EDT
Thousands of refugees return to Ukraine
Nearly 23,000 Ukrainian refugees returned to Ukraine on Saturday after fleeing the country following the Russian invasion in February, according to Ukrainian and United Nations officials.
The repatriated Ukrainians are among the more than 4.5 million who left the country between Feb. 24 and April 9, according to the U.N. High Commissioner for Refugees.
A cyclist passes by a destroyed building in the town of Borodianka, northwest of Kyiv, on April 6, 2022.
Genya Savilov/AFP via Getty Images
More than half of the Ukrainian refugees fled to neighboring Poland, officials said.
The Polish border guard service is reporting that despite the war still raging in Ukraine, the number of refugees voluntarily returning to Ukraine reached the highest figure for a single day on Saturday since the war began, according to Ukraine's Center for Strategic Communications and Information.
The UNHCR estimated that as of April 8, more than 7.1 million people in Ukraine have been displaced due to the war.
-ABC News' Christine Theodorou
Apr 10, 2022, 3:58 PM EDT
Death toll from Kramatorsk train station attack rises to 57
The death toll climbed to 57 on Sunday from an alleged Russian rocket attack Friday on a crowded train station in the eastern Ukrainian city of Kramatorsk, Ukrainian officials said.
Burnt cars are left outside a train station in Kramatorsk, eastern Ukraine, where civilians had gathered to evacuate, after it was hit by a rocket, killing scores, April 8, 2022.
Fadel Senna/AFP via Getty Images
Among those killed in the attack were five children, said Pavlo Kyrylenko, governor of the Donetsk Oblast in the Donbas region. Another 109 people were wounded when two Russian rockets struck the train station.
"There are many people in a serious condition, without arms or legs," said Kramatorsk Mayor Oleksandr Goncharenko according to the Associated Press.
The number of dead victims in the attack grew from 50 on Friday, officials said.
Ukraine's state-owned railway company issued a statement on Facebook calling the attack "a purposeful strike on the passenger infrastructure of the railway and the residents of the city of Kramatorsk."
Graphic images provided by Ukrainian officials showed the aftermath of the attack -- bodies lying on the ground next to scattered luggage and debris, with charred vehicles parked nearby.
Soldiers clear out bodies after a rocket attack killed many people on Friday, April 8, 2022, at a train station in Kramatorsk, eastern Ukraine, being used for civilian evacuations.
Fadel Senna/AFP via Getty Images
The remnants of a large rocket with the Russian words painted on its side reading "for our children" was also seen on the ground next to the main building of the train station.
Russia has denied involvement in the attack. Kremlin spokesman Dmitry Peskov claimed involvement of Russian forces was already ruled out by the Russian Ministry of Defense, based on the type of missile that was used -- a Tochka-U short-range ballistic missile.
"Our armed forces do not use missiles of this type," Peskov told reporters during a press briefing Friday. "No combat tasks were set or planned for today in Kramatorsk."
Apr 10, 2022, 2:36 PM EDT
Defense Secretary Austin holds video call with Ukrainian soldiers training in US
U.S. Defense Secretary Lloyd Austin met on Sunday via videoconference with a small group of Ukrainian troops who have been training in the United State since before Russia invaded their country on Feb. 24, according to Pentagon press secretary John Kirby.
Austin spoke to Ukrainian soldiers as the group prepared to head back to Ukraine on Sunday.
Secretary of Defense Lloyd J. Austin III speaks with Ukrainian forces via video teleconference participating in a pre-scheduled professional military education program, April 10, 2022.
Chad J. McNeeley/Department of Defense
"The Secretary thanked them for their service and for their courage, noting the skill with which the Ukrainian Armed Forces are fighting Russia's unprovoked invasion," Kirby said in a statement. "And he (Austin) pledged continued U.S. support for providing and coordinating additional security assistance."
The Ukrainians soldiers were in Biloxi, Mississippi, for naval training when the invasion began on Feb. 24. While in the United States, the U.S. Defense Department also trained the soldiers on how to use equipment the United States is sending as part of its military assistance to Ukraine, including Switchblade drones, Kirby said.
Kirby said the group spoke to Austin on Sunday from in Little Creek, Virginia, where they are "completing additional advanced tactical training."
-ABC News' Matt Seyler
Apr 10, 2022, 1:32 PM EDT
Austrian chancellor to meet with Putin
Austrian Chancellor Karl Nehammer confirmed he plans to travel to Moscow on Monday and meet with Russian President Vladimir Putin.
Nehammer noted in a Twitter post on Sunday that while Austria is militarily neutral, the country's position on Russia's war against Ukraine is that it must stop.
Austrian Chancellor Karl Nehammer meets with President Volodymyr Zelenskyy of Ukraine in an undated photo.
Nehammer said that humanitarian corridors and a ceasefire need to be established and that a full investigation should take place appraising allegations of war crimes committed by Russia in Ukraine.
The chancellor said he has notified Ukrainian President Volodymyr Zelenskyy and his European partners of his plan to meet with Putin.
Nehammer's decision to meet with Putin comes after he visited Kyiv on Saturday and met with Zelenskyy.
