Russian forces have withdrawn from key eastern towns, as a rapid Ukrainian counter-attack makes further gains.
Ukrainian officials said troops entered Kupiansk, a vital eastern supply hub for Russian forces, on Saturday.
Russia's defence ministry then said its troops have retreated from nearby Izyum to allow them "to regroup".
The ministry also confirmed the withdrawal of troops from a third key town, Balaklyia, in order to "bolster efforts" on the Donetsk front.
The Ukrainian advances - if held - would be the most significant since Russia withdrew from areas around Kyiv in April.
BBC