Russian troops are refusing to fight and the army is suffering from a "poor state of morale", according to British intelligence.
In its latest update on the war, the defence ministry said the refusal to fight "likely reflects the lack of training, motivation and high stress situations Russian forces face along the entire Ukrainian frontline".
Two soldiers were sentenced in recent days to serve at least two years in a penal colony for refusing to obey orders to return to Ukraine.
They are among the nearly 100 soldiers a week jailed for refusing to fight, according to a Russian news outlet.
The MoD said Russia is mitigating the loss by "committing a mass of poorly trained soldiers to the frontline".
"Since the September 2022 partial mobilisation, Russia has adapted its approach to warfare by utilising sheer mass for offensive and defensive operations," the MoD reported.
