Ukrainian troops are recapturing towns East of Kyiv and Russian forces, who had been trying to seize the capital are falling back on over-extended supply lines.
Britain said one of the strongest indications yet of a shift in momentum in the war.
The Mayor of Boryspol, a Suburb East of Kyiv, Volodymyr Borysenko, said Ukrainian troops had recaptured a nearby village and thousands of civilians were leaving the area in response to a call from the authorities to get out of the way of the counter-attack.
A month into their assault, Russian troops have failed to capture any major Ukrainian city.