KHARKIV, Ukraine (AP) — Ukraine kept the counteroffensive momentum in its war against Russia going Monday, saying it liberated one village after another and claiming that in one region it pushed the invaders back right up to the border in a lightning military move that stunned many.

“In some areas of the front, our defenders reached the state border with the Russian Federation,” said the regional governor of the northeastern Kharkiv region, Oleh Syniehubov. Russian troops crossed the border in the region on Feb. 24, the first day of the invasion.

Russia acknowledged the military developments by saying it was regrouping. As throughout the war, military claims were hard to verify independently.

After Sunday’s attacks by Russia on power stations and other infrastructure that knocked out electricity in many places across Ukraine, Kyiv authorities also said that electric power and water supplies have been restored to some 80 percent in the Kharkiv region.

“You are heroes!!!, wrote Kharkiv Mayor Ihor Terekhov early in the morning on Telegram, highlighting the ebullient mood in the nation that has endured more than 200 days of war and occupation. “Thanks to everyone who did everything possible on this most difficult night for Kharkiv to normalize the life of the city as soon as possible.”

The General Staff of the Armed Forces of Ukraine said that its troops had liberated more than 20 settlements within the past day.

The buoyant mood was also captured by a defiant President Volodymyr Zelenskyy on social media late Sunday, comments that immediately went viral.

“Do you still think you can intimidate, break us, force us to make concessions? Did you really not understand anything? Don’t understand who we are? What we stand for? What we are talking about,” Zelenskyy exhorted.

“Read my lips,” he continued. “Cold, hunger, darkness and thirst for us are not as scary and deadly as your ‘friendship’ and brotherhood.’”

He added: “We will be with gas, lights, water and food … and WITHOUT you!”

Yet even amid the ebullience, the casualties kept mounting. Ukraine’s presidential office said Monday that at least four civilians were killed and 11 others were wounded in a series of Russian attacks in nine regions of the country. The U.N. Human Rights Office said last week that 5,767 civilians were killed so far.

The Russians continued shelling Nikopol across the Dnieper River from the Zaporizhzhia power plant, damaging several buildings there and leaving Europe’s largest nuclear facility in a precarious position.

The turn of events and all-important reversal of initiative was backed up by international observers who warned of dire times ahead for Russian troops. It stood in sharp contrast to the first days of the war when Russian troops were moving toward Kyiv’s doorstep.

“In the face of Ukrainian advances, Russia has likely ordered the withdrawal of its troops from the entirety of occupied Kharkiv Oblast west of the Oskil River,” the British defense ministry said Monday, signifying a major advance by Kyiv. “Ukraine has recaptured territory at least twice the size of Greater London,” it said.

The British said that likely will further deteriorate the trust Russian forces have in their commanders. Ukraine’s initial move on the southern Kherson area, drawing the attention of enemy troops there, before pouncing on more depleted Russian lines in the northeast beyond Kharkiv has been seen as a great military move so far.

Even around Kherson, Russia is struggling to bring forces across the Dnipro River to stop the Ukrainian offensive there, the British military said.

It added: “The rapid Ukrainian successes have significant implications for Russia’s overall operational design. The majority of the force in Ukraine is highly likely being forced to prioritize emergency defensive actions.”

The Washington-based Institute for the Study of War said Monday that Russia likely lacks the reserve forces it needs to bolster its defenses in Ukraine.

While the war likely will stretch into next year, the institute believes that “Ukraine has turned the tide of this war in its favor” by effectively using Western-supplied weapons like the long-range HIMARS missile system and strong battlefield tactics. “Kyiv will likely increasingly dictate the location and nature of the major fighting.”

Seeking to contain its loss of momentum, Russia fired missiles at power plants and other critical infrastructure, immediately meeting with Ukrainian and U.S. criticism for centering on civilian targets.

The bombardment ignited a massive fire at a power station on Kharkiv’s western outskirts and killed at least one person. Zelenskyy denounced the “deliberate and cynical missile strikes” against civilian targets as acts of terrorism.

“Russia’s apparent response to Ukraine liberating cities and villages in the east: sending missiles to attempt to destroy critical civilian infrastructure,” U.S. Ambassador to Ukraine Bridget A. Brink wrote.

Separately, the Zaporizhzhia Nuclear Power Plant in the Russia-occupied south completely shut down in a bid to prevent a radiation disaster as fighting raged nearby.