This was reported by The New York Times with reference to the statement of the Deputy Secretary of Defense for Policy Colin Kahl and a source in the Biden administration.
"I think it's safe to assume that the Russians probably suffered 70 or 80,000 casualties in less than six months", he said.
According to him, the Russians have made some small gains in eastern Ukraine, but it has come at an extremely high cost to the Russian occupiers because of how well the Ukrainian military has performed along with the weapons they have received. Such losses mean that Putin will not be able to achieve his key goal of seizing eastern Ukraine by the end of the year.
According to intelligence, Moscow has involved Chechen military forces and fighters from Syria, whose president is an ally of Vladimir Putin. Presumably, by relying on these fighters, Putin seeks to avoid internal resentment in Russia over the losses of the Russian military and the need to conduct a general mobilization, which is similar to the draft.
According to Seth Jones, director of the international security program at the Center for Strategic and International Studies, the Russian military is severely depleted.
"This affects their ability to conduct an effective ground campaign in Ukraine", he noted.
According to American and European officials, the Russian military is suffering significant losses, and it is difficult for them to attract reservists and recruits to the battle.
The US agency adds that Russia has already committed nearly 85 percent of its military to the war, mobilizing troops from the country's far east and deploying them around the world.