Kyiv had already announced the recapture of Izyum in the country's east. (File)
Ukrainian forces said Monday their lightning counter-offensive took back yet more ground in the past 24 hours, as Russia responded with strikes on some of the recaptured areas.
The territorial shifts marked one of Russia's biggest reversals since its troops were turned back from Kyiv in the earliest days of the nearly seven months of fighting, yet Moscow signalled it was no closer to agreeing a negotiated peace.
The retreat of Russian troops in recent days has drawn weeping and relieved locals into bomb-cratered streets, including on Sunday in the strategic but heavily damaged town of Izyum.
"It's not enough to say I'm happy. I just don't have enough words to express myself," said Yuriy Kurochka, 64.
Yet by Monday Moscow had announced air, rocket and artillery attacks on reclaimed areas in the Kharkiv region, a day after Kyiv said Russian strikes on electricity infrastructure caused power failures.
The retaliatory fire came as Ukraine said forces had retaken more than 20 additional settlements, claiming "Russian troops are hastily abandoning their positions and fleeing".
Kyiv had already announced the recapture of Izyum in the country's east, while Ukraine said 3,000 square kilometers of its territory (1,158 square miles) had been prised from Russian control since September's start.
"Ukraine has turned the tide in its favour, but the current counter-offensive will not end the war," US think tank Institute for the Study of War tweeted.
Ukraine also said on Monday its forces recaptured 500 square kilometres (193 square miles) in the southern Kherson region which were in addition to the huge gains in the east at the weekend.
Defence Minister Oleksii Reznikov told French daily Le Monde, in an interview published Monday, the war has entered a new phase with the help of Western weapons.
"We started by using the HIMARS mobile artillery systems [from the US] to cut off enemy supply lines and destroy fuel and weapon depots," he reportedly said.
Moscow conceded having lost territory, which experts saw as a serious blow to its war ambitions, but Kremlin spokesman Dmitry Peskov saw no prospects for negotiations.
"The special military operation continues and will continue until the objectives that were originally set are achieved," he added, using Russia's terminology for the internationally condemned war.
Eastern parts of Ukraine were hit with widespread electricity blackouts on Sunday evening, which President Volodymyr Zelensky said deliberately hit civilian infrastructure. He blamed "Russian terrorists".
The blackouts hit regions with an estimated combined population of nine million people -- including territory controlled by Russia.
'Weapons, weapons, weapons'
The Russian strikes hit 15 locations on Sunday, from Kramatorsk in the east to Mykolaiv in the south and Dnipro in between, Ukraine's military said.
Ukraine had already lost all power from the Russian-controlled Zaporizhzhia nuclear plant, threatened by shelling since February's invasion.
The country's nuclear energy agency said the final reactor at the plant, Europe's largest nuclear power station, had been shut off as a safety measure.
Kyiv and Moscow have shown "signs that they are interested" in creating a security zone around the Zaporizhzhia plant, the UN atomic watchdog said Monday.
"What we need here really is Ukraine and Russia to agree on a very simple principle of not attacking or not shelling the plant," IAEA director general Rafael Grossi told reporters.
The speed of Ukraine's fightback has apparently caught Russia's military off-guard, bringing swathes of territory Moscow had controlled for months back into Kyiv's fold.
Images posted by the Ukrainian military showed crates of munitions and military hardware scattered across territory abandoned by Russian forces.
In his evening address Sunday, Zelensky praised the soldiers who had "liberated hundreds of our cities and villages... and most recently Balakliya, Izyum and Kupiansk".
Around Balakliya, one of the first towns to be retaken by Ukrainian troops, AFP journalists saw evidence of fierce battles, with buildings destroyed or damaged and streets mostly deserted.
The country's foreign minister used the momentum to appeal to Western allies for more stockpiles of sophisticated weapons.
"Weapons, weapons, weapons have been on our agenda since spring. I am grateful to partners who have answered our call: Ukraine's battlefield successes are our shared ones," Dmytro Kuleba said.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)