Russia's defence ministry says it has thwarted a major Ukrainian offensive in Donetsk, claiming to have killed 250 troops and destroyed 16 armoured vehicles, BBC
Video of what Russia says is the battle appears to show military vehicles coming under heavy fire in fields.
Russia's claim has not been independently verified.
And on Monday, Ukraine's military said it had no information about a major offensive in the region.
"We do not have such information and we do not comment on any kind of fake," a Ukrainian army spokesperson told Reuters.
A Ukrainian counter-offensive has been long awaited but Kyiv previously said it would not give advance warning of its start.
The Russian defence ministry said Ukraine had launched the "large-scale offensive" in the Donetsk region on Sunday using six mechanised and two tank battalions.
It claimed the Ukrainians tried to break through Russian defences in what Kyiv saw as the most vulnerable part of the front line - but that it "did not achieve its tasks, it had no success".
If the footage of armoured vehicles coming under heavy fire is authentic, then it reflects the stiff resistance Ukrainian forces will face as they try to liberate more territory.
And if it is not what it seems, it is still an attempt by Moscow to take control of the narrative.
There has been a significant increase in Ukrainian messaging on when and how their much-anticipated counter-offensive could take shape.