"There aren't any exact numbers – we've got general estimates," she told Channel 112.

"Unlike previous wars and their participants we've dealt with, now people virtually do not apply [to us] –  whether it concerns their wounded or killed. This war has turned to be very covert. We can only guess what has actually been happening on the basis of indirect data or those rare requests we receive," Melnikova said.

At the same time, she added, "there is a theoretical ratio between the losses of the belligerent states."

Read alsoAlmost 500 Ukrainian women, 70 children killed amid Russian aggression in Donbas"Therefore, our assessment is – just the way we assessed those killed and wounded in action during the first and second wars in Chechnya – and we estimate that the Russian losses (these are the so-called theoretical 'volunteers,' but in fact, they are servicemen, soldiers, officers of Russia), the death toll exceeds 1,500 men if we take the entire period of the war since the spring of 2014," she said.

Read alsoLavrov compares Crimea occupation with Falkland Islands issueAfter the annexation of Ukrainian Crimea in March 2014, Russia started destabilizing Donbas, Ukraine's east. Russia has been arming terrorists from the self-proclaimed Donbas republics and sending mercenaries and its regular troops there.

Fighting has been under way in some areas of Luhansk and Donetsk regions since the middle of April 2014.