WRAPUP 10-Ukraine forces advance on two fronts, cross Russian lines in the south

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Russian-installed official confirms Ukrainian advance in south

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Says Kyiv's forces near Dudchany, 30km from former frontline

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Ukrainian troop column heads to Lyman - Reuters witness.

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Russia sacks senior military commander

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Ukraine buoyed by weekend capture of Lyman in east

By Jonathan Landay and Tom Balmforth

SVIATOHIRSK/KYIV, Oct 3 (Reuters) - Ukrainian forces achieved their biggest breakthrough in the country's south since the war began, bursting through Russian defences and advancing rapidly along the Dnipro River on Monday, threatening supply lines for thousands of Russian troops.

In a sign Ukraine is building momentum on two fronts, 300 km to the northeast Reuters saw columns of Ukrainian troop vehicles heading to reinforce rail hub Lyman, retaken at the weekend and a staging post to press into the Donbas region.

Kyiv gave little information about the gains in the south, but Russian sources acknowledged that Ukrainian troops had advanced dozens of kilometres along the river's west bank, recapturing a number of villages along the way.

The breakthrough mirrors the recent Ukrainian successes in the east that have turned the tide in the war, 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.