Ukrainian troops have recaptured around 2,000 square km (700 square miles) of territory since it started a counter-offensive against Russia earlier this month, according to president Volodymyr Zelensky, as the Ukrainian army makes rapid advances on one of the war's principal front lines.
The Ukrainian head of state relayed the news to his people in a video address today.
It comes as Kyiv confirmed that its troops have entered the key strategic Ukrainian town of Izyum and have started clearing it.
Videos of troops at the entrance to the city circle on Telegram and Russia's Defence Ministry described the retreat as a "regrouping".
They said: "In order to achieve goals of the special military operation… a decision was made to regroup the Russian troops stationed in Balakliya and Izyum to step up efforts in the Donetsk direction."
"A three day operation was carried out to curtail and redeploy the Izyum-Balakliya troops to DPR… a number of distractions were carried out with the designation of the real actions of the troops."
Ukrainian MP Oleksiy Goncharenko said Izium was liberated in half a day and that the town of Lyman had also been freed.
He said: "Ukrainian forces entered Izum, the strategic town in the Kharkiv region. Unbelievable. In spring Russians spent 1 month to take it."
Several sources say that Izium has been liberated and military analyst Rob Lee noted two separate Russian Telegram channels 'confirmed' this was the case.
Other sources say the city has been entered by Ukrainian troops and will soon be liberated fully.
The city of Kupiansk has also been entered, as confirmed by an adviser to the head of the regional council Nataliya Popova.
Further reports suggest that Lyman is also under attack or has been captured by Ukrainian forces.
The Economist's Foreign Correspondent said there were "conflicting reports", but that "part of the picture of this counteroffensive is its speed".
The Kyiv Independent's defence reporter Illia Ponomarenko said: "The Russian front line section between Kupyansk and northern Donbas is collapsing."
He added: "An official tells me he can’t keep up. They have gone further and faster than they imagined."
Izyum is a key strategic town in the region, previously used by Russian forces as a launch pad for operations for attacks south towards Donetsk.
The success of a counter-offensive against Russia shows Ukraine can beat Moscow's forces but Kyiv needs more weapons from its partners, Foreign Minister Dmytro Kuleba said on Saturday.
Earlier on Saturday, Moscow abandoned its main bastion in northeastern Ukraine in a sudden collapse of one of the war's principal front lines after Ukrainian forces made a rapid advance.
Kuleba, speaking at a news conference with visiting German counterpart Annalena Baerbock, said some allies had initially been hesitant to send weapons, citing the risk of antagonising Russian President Vladimir Putin.
"Now, thank God, we are no longer hearing this argument ..we have demonstrated we are capable of defeating the Russian army. We are doing that with weapons given to us," he said.
"And so I reiterate: the more weapons we receive, the faster we will win, and the faster this war will end."
