KYIV, May 16 - Ukraine’s eastern city of Sievierodonetsk came under heavy shelling that killed at least 10 people, said Serhiy Haidai, the governor of the Luhansk region. In the Donetsk region, Gov. Pavlo Kyrylenko said on Facebook that nine civilians were killed in shelling.

The western Ukrainian city of Lviv was rocked by loud explosions early Tuesday. Witnesses counted at least eight blasts accompanied by distant booms, and the smell of burning was apparent some time later. An Associated Press team in Lviv, which was under an overnight curfew, said the sky west of the city was lit up by an orange glow.

Ukrainian troops also advanced as Russian forces pulled back from around the northeastern city of Kharkiv in recent days. President Volodymyr Zelenskyy thanked the soldiers who reportedly pushed them all the way to the Russian border in the Kharkiv region.

Video showed Ukrainian soldiers carrying a post that resembled a Ukrainian blue-and-yellow-striped border marker. Then they placed it on the ground while a dozen of the soldiers posed next to it, including one with belts of bullets draped over a shoulder.

I’m very grateful to you, on behalf of all Ukrainians, on my behalf and on behalf of my family,” Zelenskyy said in a video message. “I’m very grateful to all the fighters like you.”

The Ukrainian border service said the video showing the soldiers was from the border “in the Kharkiv region,” but would not elaborate, citing security reasons. It was not immediately possible to verify the exact location.

Ukrainian border guards said they also stopped a Russian attempt to send sabotage and reconnaissance troops into the Sumy region, some 90 miles (146 kilometers) northwest of Kharkiv.

Russia has been plagued by setbacks in the war, most glaringly in its failure early on to take the capital of Kyiv. Much of the fighting has shifted to the Donbas but also has turned into a slog, with both sides fighting village-by-village.

Howitzers from the U.S. and other countries have helped Kyiv hold off or gain ground against Russia, a senior U.S. defense official said. The official, who spoke on condition of anonymity to discuss the U.S. military assessment, said Ukraine has pushed Russian forces to within a half-mile to 2.5 miles (1 to 4 kilometers) of Russia’s border but could not confirm if it was all the way to the frontier.

The official said Russian long-range strikes also appeared to target a Ukrainian military training center in Yavoriv, near the Polish border. There were no immediate reports of casualties. (ap/ez)