Russia-Ukraine updates: 2 US veterans who joined Ukrainian forces missing

Russia's top general, Valery Gerasimov, spent several days in Ukraine's Donbas region last week, a senior U.S. defense official told reporters Monday.

The U.S. believes Gerasimov is now back in Russia, the official said.

The official couldn't confirm whether the general was targeted by Ukrainian forces during his visit and said the purpose of his trip is not clear to U.S. officials.

"It's certainly possible that his trip was a manner of oversight and trying to gauge for himself what was going on in the Donbas. But what he came away with, what he learned, what he transmitted to his commanders, if anything, we just don't know," the official said.

-ABC News' Matt Seyler

Valeriy Zaluzhniy, the commander in chief of Ukraine's Armed Forces, said Ukrainian troops targeted two Russian naval vessels in the Black Sea on Monday.

He shared video on his Facebook page that he says shows drones striking the boats.

Russian officials have not confirmed the strikes.

-ABC News' Irene Hnatiuk

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