Russia had arrayed approximately 120 Battalion Tactical Groups (BTGs), around Ukraine ahead of the invasion, CNN reported at the time.
Six weeks into the war, approximately 29 of those are now out of commission, the official said.
Russian forces have tried to combine some of the remaining parts of the BTGs into coherent fighting units, using the remains of two or three BTGs to attempt to make one, the official added.
Some background: The comments come a day after Kremlin spokesperson Dmitry Peskov briefly admitted on Thursday that Russia had suffered “significant” losses of its troops in Ukraine, calling it “a huge tragedy” for the country in an interview with Sky News.
Asked whether the withdrawal of Russian troops from Kyiv and its region could be seen as “a humiliation” for the Kremlin, Peskov said using those words would be “a wrong understanding of the situation.”
“We have significant losses of troops and it’s a huge tragedy for us,” Peskov admitted, before claiming the reason for Russia’s withdrawal from the Kyiv and Chernihiv regions was “an act of goodwill during the negotiations between the Ukrainian and Russian delegations.”
Peskov added that Russia did so to “lift tension from those regions in order to show Russia is really ready to create comfortable conditions for the continuation of the negotiations.”
CNN has been unable to verify how many Russian troops have been killed in Ukraine. Last month, pro-Putin Russian tabloid Komsomolskaya Pravda reported the toll was 9,861 -- multiple times higher than official figures from the Kremlin. The figure, which was attributed to the ministry and later retracted by the paper -- which claimed it was hacked -- was not confirmed by the Kremlin.
US and NATO officials estimated last month that Russian casualties range from between 3,000 to 10,000. Ukrainian officials have claimed the toll is even higher.
CNN’s Martin Goillandeau contributed reporting to this post.