More than 500 Russian troops were killed or wounded in a recent 24-hour period during the battle for the eastern Ukrainian city of Bakhmut, a Ukrainian military spokesman said on Saturday.
Pro-Moscow forces have been fighting for months to take Bakhmut, in the eastern Donbas region. Both sides admit to significant losses and the exact numbers are difficult to verify.
Serhiy Cherevaty, a military spokesperson for forces in the east, said the Russians had launched 16 attacks over a 24-hour period, with 23 clashes taking place in Bakhmut.
"Over the course of the fighting, 221 enemies were killed and 314 sustained injuries of various degrees," he told the national parliament's television channel.
It was not clear from Cherevaty's comments whether he was referring to casualties sustained on Friday or over the most recent 24 hour period.
Reuters was not able to immediately verify the claim.
An aide to Ukrainian President Volodymyr Zelenskiy said on Friday that Kyiv had decided to fight on in Bakhmut because the battle is grinding down Russia's best units.
Moscow says capturing Bakhmut would punch a hole in Ukrainian defences and be a step towards seizing all of the Donbas industrial region, a major target.
Since Russia's full scale invasion of Ukraine began in February last year, tens of thousands have been killed, millions displaced and many Ukrainian cities and towns pulverised.