By Tom Balmforth
KYIV (Reuters) -Ukrainian forces achieved their biggest breakthrough in the country's south since the war began, bursting across Russian lines on Monday and advancing rapidly along the Dnipro River, threatening supply lines for thousands of Russian troops.
Kyiv gave little information about the gains, but Russian sources acknowledged that 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," he said.
Dudchany is around 30 km (20 miles) south of where the front stood before the breakthrough, indicating the fastest advance of the war so far in the south, where Russian forces had been dug into heavily reinforced positions along a mainly static front line since the early weeks of the invasion.
While Kyiv has yet to give an account of the developments, military and regional officials did release some details.
Soldiers from Ukraine's 128th Mountain Assault Brigade raised the country's blue and yellow flag in Myrolyubivka, a village between the former front and the Dnipro, according to a video released by the Defence Ministry.
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 in a village he said was Mikhailivka, on the river bank around 20 km beyond the previous front.
Serhiy Khlan, a Kherson regional council member, also listed Osokorivka, Mykhailivka, Khreschenikvka and Zoloto Balka as villages recaptured, or where Ukrainian troops had been photographed.
"It means that our armed forces are moving powerfully along the banks of the Dnipro nearer to Beryslav," he said. "Officially, there is no such information yet, but the (Russian) social media pages which are panicking... absolutely confirm these photos."
Reuters could not immediately verify where the images of flags had been recorded. SIMILAR TACTICS TO EAST
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 a concert on Moscow's Red Square on Friday where Russian President Vladimir Putin 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.
That has opened the way for it to advance deep into Luhansk province, threatening the main supply routes to territory Moscow captured in some of the war's bloodiest battles in June and July.
In the south, Ukraine's advance targets supply lines for as many as 25,000 Russian troops on the west bank of the Dnipro. Ukraine has already destroyed the main bridges, forcing Russian forces to use makeshift crossings. A substantial advance down river could cut them off entirely.
"The fact we have broken through the front means that... the Russian army has already lost the ability to attack, and today or tomorrow it could lose the ability to defend," said Oleh Zhdanov, a military analyst based in Kyiv.
"A month of our work destroying their supplies and reducing the combat effectiveness of this group means that they are functioning on minimal rations in terms of ammunition, fuel and food."
Putin has been responding to Russia's failures on the battlefield over the past month by escalating - proclaiming the annexation of occupied territory, calling up tens of thousands of men as reservists and threatening nuclear retaliation.
But Russia's flagging fortunes have led to a shift in mood on once triumphal state media, where talkshow hosts have been acknowledging setbacks and searching for scapegoats. "For a certain period of time, things won't be easy for us. We shouldn't be expecting good news right now," said Vladimir Solovyov, the most prominent presenter on state TV.
The commander of Russia's western military district, which borders Ukraine, has lost his job, Russian media reported on Monday, the latest in a series of top officials to be fired after the defeats.
Ramzan Kadyrov, the pro-Putin leader of Russia's Chechnya province who commands a personal army, demanded the commander of Russian forces in eastern Ukraine be stripped of his medals and sent to the front line.
Kadyrov also said Russia should use a nuclear weapon. Putin and other officials have said they could use nuclear weapons to protect Russian territory including newly annexed provinces, but had so far stopped short of explicitly saying they will do so.
Asked about Kadyrov's remarks, Kremlin spokesman Dmitry Peskov said: "This is a very emotional moment."
"Even at difficult moments, emotions should still be excluded from any assessments," he added. Putin's other big gamble, Russia's first mass military mobilisation since World War Two, has been mired in chaos. Tens of thousands of Russian men have been called up, while similar numbers have fled abroad. Western countries say Moscow lacks the supplies and manpower to train or equip the new conscripts.
Mikhail Degtyarev, governor of the Khabarovsk region in Russia's Far East, said on Monday around half of those called up there had been found unfit and sent home. He fired the region's military commissar.