The UK said Russia had deployed nearly all of its military to Ukraine, increasing pressure on frontlines in eastern Ukraine, but without achieving a breakthrough.
Ukrainian officials have warned of a new Russian offensive to mark the first anniversary of the invasion next week.
However, some Western officials doubt the offensive is a one-time event.
“We estimate that 97% of all Russian military is in Ukraine,” British Defense Secretary Ben Wallace told the BBC’s Today programme.
Russian forces are trying to advance on all fronts, he said.
“We have not seen such a concentration of forces make a big offensive. We saw an offensive attempt, and it cost the Russian military dearly,” Wallace added.
