Ukrainian forces have achieved their biggest breakthrough in the south of the country since the war began, bursting through the front, advancing rapidly along the Dnipro River and threatening to encircle thousands of Russian troops.

Kyiv gave no official confirmation of the gains, but Russian sources acknowledged a Ukrainian tank offensive had advanced dozens of kilometres along the river’s west bank, recapturing a number of villages along the way.

The breakthrough mirrors recent Ukrainian successes in the east that have turned the tide in the war against Russia, even as Moscow has tried to raise the stakes by annexing territory, ordering mobilisation and threatening nuclear retaliation.

“The information is tense, let’s put it that way, because, yes there were indeed breakthroughs,” Vladimir Saldo, the Russian-installed leader in occupied parts of Ukraine’s Kherson province told Russian state television.

“There’s a settlement called Dudchany, right along the Dnipro River, and right there, in that region, there was a breakthrough. There are settlements that are occupied by Ukrainian forces.”

Dudchany is 40 kilometres south of where the front stood a day earlier, indicating one of the fastest advances of the war and by far the most rapid in the south, where Russian forces were dug into heavily reinforced positions along a mainly static front line since the early weeks of the invasion.

Anton Gerashchenko, an adviser to Ukraine’s interior ministry, posted a photo of Ukrainian soldiers posing with their flag draping a golden statue of an angel.

He said it was the village of Mikhailivka, 20 kilometres beyond the previous front.

“In the last days, we have seen the first photo of Osokorivka … we have seen our troops near the entrance to Mykhailivka, we have seen our troops in Khreschenivka, next to the monument,” Serhiy Khlan, a Kherson regional council member, told Reuters.

The advance in the south mirrors the tactics that have brought Kyiv major gains since the start of September in eastern Ukraine, where its forces swiftly seized territory to gain control of Russian supply lines, cutting off larger Russian forces and forcing them to retreat.

Just hours after Russian President Vladimir Putin on Friday proclaimed the provinces of Donetsk, Luhansk, Kherson and Zaporizhzhia to be Russian territory forever, Ukraine recaptured Lyman, the main Russian bastion in the north of Donetsk province.

Mr Putin has responded to Russia’s failures on the battlefield in the past month by escalating – proclaiming the annexation of occupied territory, calling up tens of thousands of men as reservists and threatening nuclear retaliation.

In the south, Ukraine’s advance targets supply lines for thousands of Russian troops – perhaps as many as 25,000 – on the west bank of the Dnipro, where it sent a large contingent to halt a counter-attack Ukraine announced there in August.

The reports of Ukraine’s battlefield advances have come amid chaos back in Russia over the mobilisation, which Mr Putin ordered 10 days ago.

Tens of thousands of Russian men have been called up, while tens of thousands of others have fled abroad.

Mikhail Degtyarev, governor of the Khabarovsk region in Russia’s Far East, said on Monday half of the men called up there had been found unfit for duty and sent back home.

He fired the region’s military commissar.

-Reuters