Ukraine's stunning offensive has "snowballed" as the country's chief commander says forces have now recaptured 3,000 square kilometres from Putin's army since the start of the month.
Their reinvigorated forces kept pushing north in the Kharkiv region and advancing to its south and east, Ukraine's army chief has said - a day after their rapid gains forced Russia to abandon its main bastion in the area.
It comes after the country's President Volodymyr Zelensky announced that the "entire Donetsk region will be liberated" and that "about 2,000 kilometres of our territory have already been liberated" in just 48 hours, around 770 square miles in the Kharkiv region.
The disinformation campaign appears to have successfully distracted Russia, experts say.
Zelensky, 44, hailed Ukraine's offensive as a potential breakthrough in the six-month-old war, saying this winter could bring more rapid gains of territory if Kyiv can get more powerful weapons.
Russia had already suffered around 60,000 casualties, it was announced last month.
Ukraine's chief commander, General Valeriy Zaluzhnyi, said on Sunday that the armed forces had regained control of more than 3,000 square km (1,158 square miles) since the start of this month.
"In the Kharkiv direction, we began to advance not only to the south and east, but also to the north. There are 50 km to go to the state border (with Russia)," he said on Telegram.
In Moscow, Russia's defence ministry said Russian forces were hitting Ukrainian army positions in the Kharkiv region with precision strikes by airborne troops, missiles and artillery.
The retreat from the city of Izium, an important logistics hub for Russian forces, was their worst defeat since they were repelled from the capital Kyiv in March, as thousands of Russian soldiers left behind ammunition and equipment as they fled.
Moscow's almost total silence on the defeat - or any explanation for what had taken place in northeastern Ukraine - provoked significant anger among some pro-war commentators and Russian nationalists on social media. Some of them called on
Sunday for President Vladimir Putin to make immediate changes to ensure ultimate victory in the war.
Ukraine's gains are important politically for Zelenskiy as he seeks to keep Europe united behind Ukraine - supplying weapons and money - even as an energy crisis looms this winter following cuts in Russian gas supplies to European customers.
"I believe that this winter is a turning point, and it can lead to the rapid de-occupation of Ukraine," Zelenskiy told a political forum. "If we were a little stronger with weapons, we would de-occupy faster," he said in remarks published on his website late on Saturday.
Ukrainian officials stopped short of confirming they had recaptured Izium, but Zelenskiy's chief of staff Andriy Yermak posted a photo of troops on its outskirts and tweeted an emoji of grapes. The city's name means "raisin."
Defence minister Oleksii Reznikov said Ukraine needed to secure retaken territory against a possible Russian counterattack on stretched Ukrainian supply lines.
He told the Financial Times that Ukrainian forces could be encircled by fresh Russian troops if they advanced too far.
But he said the offensive had gone far "better than expected", describing it as a "snowball rolling down a hill".
"It's a sign that Russia can be defeated," he said. Kyiv-based military analyst Oleh Zhdanov said the gains could bring a further push into Luhansk region, whose capture Russia claimed at the beginning of July.
"If you look at the map, it is logical to assume that the offensive will develop in the direction of Svatove - Starobelsk, and Sievierodonetsk - Lysychansk," he said.
Britain's defence ministry said on Sunday Ukrainian forces had made gains in the Kharkiv region over the past 24 hours.
But fighting continued around Izium and the city of Kupiansk, the sole rail hub supplying Russia's front line across northeastern Ukraine, which has been retaken by Ukraine's forces.
As the war entered its 200th day, Ukraine reported more Russian missile and air strikes overnight and regional officials reported heavy Russian shelling in the east and south.
