“Despite small-scale initial advances, Russia has failed to achieve substantial territorial gains over the past month whilst sustaining consistently high levels of attrition,” the British defence ministry said on Twitter.
“Russia has now likely suffered losses of one third of the ground combat force it committed in February.”
It said Russia was unlikely to dramatically accelerate its rate of advance over the next 30 days.
Since Russia’s invasion on February 24, Ukraine’s military has forced Russia’s commanders to abandon an advance on the capital Kyiv, before making rapid gains in the northeast and driving them away from the second biggest city of Kharkiv.
A Ukrainian counteroffensive has been under way near the Russian-held town of Izium, though Ukraine’s military reported on Sunday that Russian forces were advancing elsewhere in the Donbas region, the main theatre of war over the past month.