Ukrainian forces have swept further across territory seized from fleeing Russian troops, as Moscow grapples with the consequences of the collapse of its occupation force in northeastern Ukraine.

Ukraine’s general staff said early on Monday that its forces had recaptured more than 20 towns and villages in just the past day, after Russia acknowledged it was abandoning Izium, its main stronghold in northeastern Ukraine.

“Taking them under full control and stabilisation measures are being carried out,” the general staff said of the newly re-captured settlements.

As thousands of Russian troops abandoned their positions, leaving behind huge stocks of ammunition and equipment, Russia fired missiles at power stations on Sunday causing blackouts in the Kharkiv and adjacent Poltava and Sumy regions.

• Ukraine’s nuclear power plant shuts down (11 September)
• Ukraine retakes territory in Kharkiv area (10 September)

Ukraine denounced what it described as retaliation against civilian targets for its military advances.

By Monday morning, Reuters journalists in Kharkiv said the power was back on, although the water was not yet working. The regional governor said power had been restored by 80 per cent. 

Britain’s ministry of defence said Russia had probably ordered its forces to withdraw from all of Kharkiv region west of the Oskil River, abandoning the main supply route that had sustained Russia’s operations in the east.

Kyiv, which reached the Oskil when it seized the railway hub city of Kupiansk on Saturday, suggested Russia was already falling even further back; the Ukrainian general staff said Russian troops had abandoned Svatove in Luhansk province, about 20 km east of the Oskil. 

The British ministry said Moscow’s forces were also struggling to bring reserves to the frontline in the south, where Ukraine has launched a big advance in Kherson province aiming to isolate thousands of Russian soldiers on the west bank of the Dnipro River.

Ukraine’s swiftest advance since driving Russian forces away from the capital in March has turned the tide in the six-month war, unravelling in a matter of days swathes of the gains Moscow had achieved in months of costly fighting in the east.

Ukrainian chief commander General Valeriy Zaluzhnyi said his troops had retaken more than 3000 sq km this month, advancing to within 50 km of the border with Russia.

Further Russian retreats, especially east of the Oskil, could soon put Ukrainian forces in position to attack territory that Russia and its local proxies had held since 2014.

Denis Pushilin, leader of the pro-Russian separatist proxy administration in Donetsk province, acknowledged pressure from multiple directions.

Moscow has so far remained largely mute since its frontline collapsed in the northeast last week, with President Vladimir Putin and his senior officials withholding any comment on the “special military operation” they have always said was “going to plan”.

After days of making no reference at all to the retreat, Russia’s ministry of defence acknowledged on Saturday that it had abandoned Izium and neighbouring Balakliia, in what it called a pre-planned “regrouping” to fight in Donetsk.

Russian broadcasters, required by law to report only official accounts, have alluded to the setbacks but struggled to explain them, with commentators mainly demanding a redoubled war effort.

“We must win the war in Ukraine! We must liquidate the Nazi regime!” one commentator said on a panel show on NTV television.

“And how many years is that supposed to take?” replied another. “So my 10-year-old children will get a chance to fight?”

By Pavel Polityuk and Tom Balmforth in KYIV/KHARKIV