Ukrainian forces have broken through Russian defenses in the south of the country while expanding their rapid offensive in the east, seizing back more territory in areas annexed by Russia and threatening its troops' supply lines.

Making their biggest breakthrough in the south since the war began, Ukrainian forces recaptured several villages in an advance along the strategic Dnipro River on Monday, Ukrainian officials and a Russian-installed leader in the area said.

Ukrainian forces in the south destroyed 31 Russian tanks and one multiple rocket launcher, the military's southern operational command said in a nightly update, without providing details of where the fighting occurred.

Battlefield accounts could not be confirmed immediately

The southern breakthrough mirrors recent Ukrainian advances in the east even as Russia has tried to raise the stakes by annexing land, ordering mobilization, and threatening nuclear retaliation.

Ukraine has made significant advances in two of the four Russian-occupied regions Moscow last week annexed after what it called referendums – votes that were denounced by Kyiv and Western governments as illegal and coercive.

In a sign Ukraine is building momentum on the eastern front, Reuters saw columns of Ukrainian military vehicles heading on Monday to reinforce the rail hub of Lyman, retaken at the weekend, and a staging post to press into the Donbas region.

President Volodymyr Zelenskyy said Ukraine's army had seized back towns in a number of areas, without giving details.

"New population centers have been liberated in several regions. Heavy fighting is going on in several sectors of the front," Zelenskyy said in a video address.

Serhiy Gaidai, the governor of Luhansk – one of two regions that make up Donbass – said Russian forces had taken over a psychiatric hospital in the town of Svatovo, a target en route to recapturing the major cities of Lysychansk and Sivierodonetsk.

"There is quite a network of underground rooms in the building and they have taken up defensive positions," he told Ukrainian television.

In the south, Ukrainian troops recaptured the town of Dudchany along the west bank of the Dnipro River, which bisects the country, Vladimir Saldo, the Russian-installed leader in occupied parts of Ukraine's Kherson province, told Russian state television.

"There are settlements that are occupied by Ukrainian forces," Saldo said.

Dudchany is about 30 kilometers (20 miles) south of where the front stood before Monday's breakthrough, indicating the fastest advance of the war in the south. Russian forces there had been dug into heavily reinforced positions along a mainly static front line since the early weeks of the invasion.

While Ukraine has yet to give a full account of the developments, military and regional officials did release some details.

Soldiers from Ukraine's 128th Mountain Assault Brigade raised the blue and yellow national flag in Myrolyubivka, a village between the former front and the Dnipro, according to a video released by the defense ministry.

Serhiy Khlan, a Kherson regional council member, listed four other 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.

Russian missiles struck the northeastern city of Kharkiv killing a woman, its governor said on a messaging service, while Ukraine's General Staff said Russian reinforcements were arriving from Siberia and Syria.

Reuters was unable to verify the developments.

Ability to attack

The southern advance is targeting supply lines for as many as 25,000 Russian troops on the Dnipro's west bank. Ukraine has already destroyed the river's main bridges, forcing Russian forces to use makeshift crossings.

A substantial advance downriver 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.

Ukraine appears to be on course to achieve several of its battlefield objectives, giving it "a much better defensive position to ride out what probably will be a tamping down of the hot fighting over the winter," Celeste Wallander, a senior Pentagon official, said on Monday.

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.

Billionaire Elon Musk on Monday asked Twitter users to weigh in on a plan to end the war which included proposing U.N.-supervised elections in the four occupied regions and recognizing Crimea, which Moscow seized in 2014, as Russian.

The plan drew immediate condemnation from Ukrainians, including Zelenskyy.

Russia's flagging fortunes have led to a shift in mood on state media, where talk show 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 television.

The commander of Russia's western military district, which borders Ukraine, has lost his job, Russian media reported, the latest top official to be fired after defeats.