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”.

At a meeting of Nato foreign ministers in Berlin, the foreign secretary, Liz Truss, said it was essential to maintain support for the government in Kyiv to help it “push Russia out”.

She said in a statement: “Putin must face a sustained defeat in Ukraine, Russia must be contained and such aggression must never happen again.