Russia's defense ministry says its forces, together with the Russian private military firm the Wagner Group, have taken full control of the Ukrainian city of Bakhmut in the eastern region of Donetsk.
But Ukraine refutes that claim, saying that the fighting there is ongoing.
The Russian defense ministry made the announcement in a social media post early Sunday.
That followed a social media post on Saturday by Wagner leader Yevgeny Prigozhin saying that his troops have taken Bakhmut and would pull out on Thursday or later.
Russia and Ukraine have been locked in fierce fighting over Bakhmut.
Russia wanted to take full control of the region. It considers Bakhmut a foothold for the nearby city of Slovyansk, one of Ukraine's operation bases.
A Ukrainian military spokesperson for the eastern front told the Reuters news agency on Saturday that the Russian claim is not true and that Ukrainian units are fighting there.
Ukraine's Deputy Defense Minister Hanna Maliar also rejected the Russian claim, writing in a social media post that the situation is critical but that Ukrainian troops there are maintaining a defense.