Kyiv's defense ministry claims that more than 5,000 Russian soldiers have been killed in the first four days of fighting in Ukraine, BBC reported.
In a statement posted to Facebook, Ukrainian officials said approximately 5,300 Russian troops have been killed, and claimed that 191 tanks, 29 fighter jets, 29 helicopters and 816 armoured personnel carriers have been destroyed by Ukraine's forces.
The BBC has not been able to independently verify these claims, though the UK's Ministry of Defence believes Russia has taken "heavy" casualties in the opening stages of the conflict.
The claims follow acknowledgements by the Russian defence ministry on Sunday that its forces have suffered losses, though officials did not provide an exact figure, BBC reported.
Meanwhile, UN observers said they had confirmed at least 94 civilian deaths during the first four days of fighting.
It said the invasion had triggered "severe humanitarian consequences" and that casualties could be considerably higher.