Russia claims to have killed 250 Ukrainian soldiers while the Kremlin’s forces successfully pushed back a major offensive in the Donetsk region.
Moscow claimed Ukraine had lost 250 troops as well as 16 tanks.
This claim hasn't been independently verified nor has footage released by Moscow appearing to show military equipment being destroyed.
A video of what Russia says is the battle appears to show military vehicles coming under heavy fire in fields.
Commander of Ukraine's ground forces Oleksandr Syrskyi said on Monday that Ukrainian forces continued "moving forward" near the long-contested city of Bakhmut in northern Donetsk.
Ukraine's Centre for Strategic Communications did not address the Russian statement directly but said that Russia would seek to spread lies.
Experts have been waiting for a counter-offensive for weeks and it remains to be seen if this was the start of it.
Former Joint Forces Commander Sir Richard Barrons said this counter-offensive would not have a long-term impact on the war.
“Whenever this counter offensive comes, nobody really thinks it's going to throw all the Russians out of Ukraine,” he said.
“We should see this offensive as just part of a long war, and it should set the scene for more strategic support to Ukraine.”