Still, with all of that loss, the US assesses that Russians “still have the … majority of their capability left to them,” the official added. “They have invested an awful lot of their hardware and their personnel in this fight, and the Ukrainians have suffered losses, the Russians have suffered losses."

“Russians do have a superiority here in terms of number of assets they can apply to this fight in terms of people, and equipment and weapons, and we just have to bear that in mind,” the official added.

Russia may have lost a third of the invasion force it sent into Ukraine as its offensive continues to struggle in the face of stiff resistance, British military intelligence has said.

In its latest assessment, the Ministry of Defence (MoD) said the Russian campaign in the east of Ukraine had “lost momentum” and was now “significantly behind schedule”.