Ukraine has reclaimed vast swathes of territory in the eastern region after a rapid counter-offensive forcing the retreat of Russian forces.
President Volodymyr Zelensky said his forces were now working on fortifying their hold over 8,000 sq km of retaken territory in the Kharkiv region.
While Russia still controls around a fifth of Ukraine's territory, towns in the Donbas that fell early in the war are now under threat from Kyiv's advancing forces.
The Kremlin has admitted that its forces have moved out of some eastern towns, but refused to call it a retreat, instead insisting that its forces are regrouping.
On Monday, Moscow insisted that it would press on with its invasion "until all the goals that were originally set are achieved", The BBC reports.
Russia's full-scale invasion started more than six months ago,despite the territorial regain by Ukrainian forces, commentators have noted that the conflict will be drawn out.
US President Joe Biden said Ukraine had made "significant" gains.
Mr Biden said it was "clear" that the advance had enjoyed success, but cautioned that the offensive "could be a long haul".
Read more at the BBC
