Ukraine says it has pushed Russian forces back up to five miles (8km) from the Dnipro River after establishing bridgeheads on its eastern bank.
If confirmed, the strategic advance would be one of the most significant in recent months after little gains from either side in the war in Ukraine.
Kyiv says its forces are now battling for control of three Russian-occupied villages south of the river.
A win there would not only be an important military breakthrough but also offer an important morale-boost ahead of winter.
However, Ukrainian officials said its soldiers still had “a lot of work to do” to establish their positions and warned that the bridgehead was fragile.
“Preliminary figures vary from three to eight kilometres, depending on the specifics, geography and landscape design of the left bank,” army spokeswoman Natalia Gumenyuk told Ukrainian television of the territory that its soldiers claimed to have captured.
The Kremlin’s Ministry of Defence corroborated Kyiv’s claims, saying that Ukrainian marines had crossed the Dnipro River roughly 20 miles upstream from Kherson City, but said Russian artillery was now pounding the area.
WarGonzo, a pro-war Russian military Telegram blog with 1.1 million subscribers, said fighting was focused on the villages of Poima, Peschanivka and Krynki.
“The Russian armed forces are trying to retake the Ukrainian bridgehead on the left bank of the Dnipro,” the channel reported.
Seizing the villages would be an important win for Ukraine as it tries to turn round its largely disappointing counter-offensive and convince western backers their money has not been wasted.
‘Putin may be feeling chipper’
But analysts earlier warned that even if a bridgehead were established, Ukraine now faces an adversary in Vladimir Putin, the Russian president, who has been emboldened by his troops’ ability to stymie the counter-offensive.
“Putin may actually be feeling chipper as he looks ahead to 2024 with his mood steadily improving since the Ukrainian offensive was stillborn in June,” said John Foreman, Britain’s former defence attaché in Moscow and a military analyst.
The British Ministry of Defence agreed that the war in Ukraine had ground to a stalemate. It said the onset of winter in Ukraine means there is likely to be little progress by either army anywhere along the front line.
This includes Avdiivka on the eastern front line, where the Kremlin has committed tens of thousands of soldiers to try to break through Ukrainian lines, in what has been described as the deadliest battle of the year.
Estonian military intelligence said Ukrainian forces had built robust defences in the town, which was now nearly surrounded by Moscow’s troops.
“It is most likely that Russian forces will make every effort to avoid entering the city,” it said. “The Russian aim consists of encircling Avdiivka and its garrison.”
For the past couple of nights, dozens of Iranian-made Shahed drones have attacked Kyiv, in what observers said marked the resumption of the Kremlin’s strategy to cripple Ukraine’s electricity and heating infrastructure ahead of winter.
Ukrainian forces said that they shot down 15 out of 20 drones on Saturday evening. No casualties were reported.