The Russian military has lost a significant portion of its ground forces in Ukraine since invading nearly three months ago while its latest offensive has stalled, according to the United Kingdom's Defense Ministry.

Russia has lost roughly a third of the ground combat forces that were committed to the Ukraine fight, the agency said on Sunday, adding that Moscow's forces have sustained “consistently high levels of attrition.”

The update from the U.K. on Russia’s remaining capacity comes a couple weeks after the Pentagon had assessed that the Russians have lost 25% of their capabilities, though a senior defense official told reporters last week that they’re no longer keeping track.

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Russian forces, after their initial efforts to capture the capital of Kyiv failed and they were forced to retreat, have since refocused their military efforts to the Donbas region, which is the part of eastern Ukraine near Russia. There has been fighting for nearly a decade in the region between Ukrainians and pro-Russian separatists.

The Russians' attempts to capture Kyiv were thwarted by Ukrainian forces, which put up a much stronger resistance than expected, in addition to their own problems such as low morale and supply shortages, though many of those problems have continued to their new phase.

The Donbas offense “has lost momentum and fallen significantly behind schedule,” the ministry said in an update. “Despite small-scale initial advances, Russia has failed to achieve substantial territorial gains over the past month," adding that the delays "will almost certainly be exacerbated by the loss of critical enablers such as bridging equipment and intelligence, surveillance and reconnaissance drones."

Ukraine's general staff said that Russian troops were withdrawing from Kharkiv, Ukraine’s second-largest city.

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"I am grateful to everyone who holds the line and brings closer to Donbas, Pryazovia, and Kherson the same thing that is happening now in the Kharkiv region," Ukrainian President Volodymyr Zelensky said on Saturday. "Step by step we are forcing the occupiers to leave our land. We will make them leave the Ukrainian sea as well."

Ukrainian forces ”prevented Russian troops from encircling, let alone seizing Kharkiv, and then expelled them from around the city as they did to Russian forces attempting to seize Kyiv,” the Institute for the Study of War’s Friday assessment read.