Russia’s gains on the battlefield in Ukraine have slowed dramatically in recent months, largely owing to Ukraine’s improved drone tactics and defences, according to Western intelligence and analysis.

Russia’s territorial gains amount to five times less than they were five months ago, with casualty rates rising from Moscow’s attempts to break through Kyiv’s defences, a senior Nato official said.

Western officials and analysts say Ukraine was able to stall Russia’s potentially war-winning offensive in the east of the country through a combination of improved drone tactics and defences.

Moscow’s advances have also been bogged down by cold winter months and combat in built-up areas.

George Barros, of the Institute for the Study of War, said the length of Russia’s offensive is taking its toll on its soldiers. “When you continue fighting after the point in which you’ve been exhausted and the point at which your forces offensive operations are culminated, you can keep fighting, but you’re going to get diminishing marginal returns. Your attrition rate is going to go higher, and you’re just not going to be quite as effective,” he said.