President Volodymyr Zelensky has been to the recaptured city of Izyum, a key logistics hub in north-eastern Ukraine.
During his visit, Mr Zelensky thanked troops who took part in the counter-attack against Russian occupiers.
He oversaw a flag-raising ceremony and said the Ukrainian flag would return to every city and village in the country.
Ukrainian officials say they are targeting towns in the eastern Donbas region after making a series of gains in a rapid counter-offensive.
In recent days, Ukraine's army has reclaimed swathes of occupied territory, forcing Russian troops to retreat.
In a late evening address on Tuesday, Mr Zelensky said his forces were fortifying their hold over 8,000 sq km (3,088 sq miles) of retaken territory in the Kharkiv region.
Last Thursday, President Zelensky said Ukrainian forces had retaken 1,000 sq km. By Sunday, that stated figure had tripled to 3,000 sq km, before rising again to 6,000 sq km.
The precise scale of Ukraine's gains has not been verified by the BBC.
He vowed to take back all Ukrainian territory still occupied by Russian forces - he said he did not know when this would happen, but that the "truth is on our side".
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".
https://www.bbc.co.uk/news/world-europe-62899474