The Lysychansk Gymnasium, an acclaimed secondary school in Ukraine's Luhansk region, burned to the ground after coming under fire in targeted shelling, said Serhiy Haidai, the head of Luhansk's Regional Military Administration. The school was more than a century old.

-ABC News' Max Uzol and Irene Hnatiuk

Ukrainian forces have carried out an offensive in the country's Kharkiv region, taking back control of several settlements, Ukraine's Ministry of Defense said Monday. This includes the settlements of Verkhnya Rohanka, Ruska Lozova, Slobidske and Prilesne.

-ABC News' Irene Hnatiuk

U.S. Embassy staff returned to Ukraine for the day on Monday, marking the first trip back in the country since February.

"We expect to continue to do day trips for the next week or two and we very much hope that the conditions will permit us to go back to Kyiv by the end of the month," Kristina Kvien, the U.S. chargé d'affaires to Ukraine, said in a statement.

Kvien said, "The message to Russia is: you failed -- Ukraine is still standing, the government is still functioning and we are going back to Lviv first and then Kyiv to help the government."

Kvien continued, "We are listening to the security professionals and when they tell us we can go back we go back. And while we are eager to do so we also want to make sure we are listening to the experts. So, the fact that we are here in Ukraine means that the security officials just said that it is ok and safe to meet here in Lviv and hopefully we will get the clearance to go back to Kyiv."

-ABC News' Clark Bentson

Dozens of civilians trapped for weeks inside a steel plant in the devastated Ukrainian city of Mariupol were expected to reach Zaporizhzhia on Monday, according to Ukrainian President Volodymyr Zelenskyy.

In a statement posted to Twitter on Sunday, Zelenskyy said a first group of about 100 people were already en route to the Ukrainian government-controlled city, about 140 miles northwest of Mariupol.

"Tomorrow we'll meet them in Zaporizhzhia," Zelenskyy tweeted. "Grateful to our team!"

Many more civilians remain trapped at the sprawling Azovstal Iron and Steel Works plant in Mariupol -- the last holdout of Ukrainian resistance to Russia's bombardment of the strategic southeastern port city -- which Russian forces resumed shelling overnight.

"Today, for the first time in all the days of the war, this vitally needed green corridor has started working," Zelenskyy said Sunday in his nightly address.

Jalina Porter, the State Department's deputy spokesperson, is responding to the Russian attack at a Ukraine train station that killed at least 50, saying, "We can no longer be surprised by the Kremlin's repugnant disregard for human life."

Five children were among those killed when Russian rockets struck the station in Kramatorsk in Donetsk Oblast on Friday morning, according to Ukraine's state-owned railway company. At least 100 people were injured, according to Donetsk Oblast Gov. Pavlo Kyrylenko.

Russia has denied involvement in the attack, which occurred as "thousands" of civilians fleeing the Russian invasion were at the train station waiting to be taken to "safer regions of Ukraine," according to Kyrylenko.

"Civilians are killed when they stay in their homes, and they're killed when they try to leave," Porter said. "Actions like these demonstrate why Russia did not belong on the U.N. Human Rights Council, and they also reinforce the U.S. assessment that members of Russian forces are committing war crimes in Ukraine."

Porter declined to say if the department considers the train station attack a war crime, saying, "Assessing individual criminal liability in specific cases is the responsibility of courts, as well as other investigatory bodies. But as the secretary, Secretary [of State Antony] Blinken, has said, 'Those responsible for war crimes and other atrocities committed in Ukraine will be held to account.'"

-ABC News' Conor Finnegan