Russia’s offensive in the Donbas region in Ukraine’s east “has lost momentum and fallen significantly behind schedule,” British military intelligence says.

Russia has now likely suffered losses of one-third of the ground combat force it committed in February, the British Ministry of Defense said in a regular bulletin on May 15.

After failing to capture Kyiv following the February 24 invasion, Russia has shifted its focus to the Donbas, an area comprising the Luhansk and Donetsk regions.

Meanwhile, Ukraine’s military said it had launched a counteroffensive near the eastern, Russian-held town of Izyum as Kyiv said Kremlin forces were withdrawing from areas near Kharkiv, Ukraine’s second-largest city, in what appears to be the latest setback for Moscow’s military offensive.

Ukraine’s General Staff said on May 14 that Russian forces appeared to be focusing on guarding supply routes and were launching mortar, artillery, and air strikes in the Donetsk region in an effort to “deplete Ukrainian forces and destroy fortifications.”

Defense Minister Oleksiy Reznikov said Ukraine was “entering a new — long-term — phase of the war.”

Britain said that despite small-scale initial advances, Russia had failed to achieve substantial territorial gains in Donbas over the past month while sustaining consistently high levels of attrition.

Russian forces are increasingly constrained by degraded enabling capabilities, continued low morale, and reduced combat effectiveness, the ministry said.

“Many of these capabilities cannot be quickly replaced or reconstituted, and are likely to continue to hinder Russian operations in Ukraine,” the bulletin added.

The ministry predicts that under the current conditions, Russia is unlikely to dramatically accelerate its rate of advance over the next 30 days.

Meanwhile, U.S. Senate Republican leader Mitch McConnell led a delegation of Republican senators on a surprise visit to Kyiv in a show of support for Ukraine in its fight against the unprovoked Russian invasion.

The McConnell-led trip, which followed one by Democratic House of Representative leaders on May 1, comes as the Senate attempts to finalize a $40 billion military aid package for Ukraine.