US President Joe Biden is due to visit Poland on Monday to mark the first anniversary of Russia's invasion of neighbouring Ukraine, which said it was inflicting heavy losses on Moscow's forces.
The war which began on February 24 last year has cost hundreds of thousands of lives, driven millions from their homes and reduced cities to rubble across swathes of southern and eastern Ukraine.
There has been little change on the vast frontline in recent months as both sides prepare for offensives expected in the spring, Russia boosted by thousands of conscripts and Ukraine fortified with Western battle tanks.
Ukrainian President Volodymyr Zelenskiy said on Sunday that Russia had suffered "extraordinarily significant" losses near the town of Vuhledar in the eastern Donbas region, which Moscow claimed to have annexed in September.
"The situation is very complicated. And we are fighting. We are breaking down the invaders and inflicting extraordinarily significant losses on Russia," Zelenskiy said in his nightly video address.
He referred to several towns where fighting has been focused for months, saying "the more losses Russia suffers there, in Donbas - in Bakhmut, Vuhledar, Marinka, Kreminna - the faster we will be able to end this war with Ukraine's victory".
Russia's defence ministry said on Saturday that its forces had captured Hrianykivka, a village in the eastern Kharkiv region that is well to the north of the hottest part of the front, which is around Bakhmut.
Ukraine's General Staff on Monday said its forces "repelled Russian attacks in the areas of the Hrianykivka village", but that the Russians continued to heavily shell the area with artillery.
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