Russia said Wednesday for the first time that some Ukrainian troops had established positions on the Moscow-held side of the Dnipro river, the vast waterway that splits the frontline in southern Ukraine.
The admission came as President Volodymyr Zelensky said it had been a "difficult day" for Kyiv due to deadly Russian strikes in the east of the country.
A sustained Ukrainian breakthrough across the river would mark a significant tactical success for Kyiv, whose wider counteroffensive has so far failed to turn the tide of the 21-month war.
"Small groups" of Ukrainian soldiers were stretched along the eastern bank of the Dnipro river, and had been "blocked" in the tiny village of Krynky, the Moscow-installed head of Ukraine's Kherson region, Vladimir Saldo, said in a post on Telegram.
But he insisted they were facing a "fiery hell" from Russian artillery, rockets and drones, and were suffering heavy losses.
Russian and Ukrainian forces have been entrenched on opposite sides of the Dnipro river since Moscow withdrew from the western part of Kherson region last November.
That was the last major territorial change in the conflict, with both sides having since failed to make progress despite staging multiple offensives.
Russia's Saldo said Wednesday that "about one and a half enemy companies, mostly in small groups," were currently on the Russian-held side.
According to Russia's TASS news agency, a company in the Russian military consists of anything from 45 to 360 soldiers.
- 'Fiery hell' -
"Our additional forces have now been deployed. The enemy is blocked in Krynky. A fiery hell has been arranged for them: bombs, rockets, heavy flamethrower systems, artillery shells and drones are flying at them," Saldo said.
His comments were the first admission by a senior Russian official that Ukraine had managed to secure some positions on the Russian-controlled side of the river.
AFP was not able to verify his reports and the scale of Ukraine's crossing was unclear.
Since mid-October, Russian military bloggers close to the armed forces have been reporting that small groups of Ukrainian troops were successfully crossing the river.
The Kremlin earlier this week refused to comment, deferring questions to the defence ministry.
The ministry has said separately that it had captured a small group of Ukrainian soldiers "trying to land on the left bank".
Both Kyiv and Moscow regularly claim to have killed high numbers of "enemy" soldiers, though neither side comments on their own losses.
Despite a relatively static frontline, both Kyiv and the Kremlin have denied the conflict has ground to a stalemate.
Andriy Yermak, Zelensky's chief of staff, said Tuesday Ukrainian forces had "gained a foothold on the left bank of the Dnipro," without providing details.
Krynky, where Saldo said the Ukrainians had been trapped, is a small village 35 kilometres (22 miles) to the east and upstream of the city of Kherson.
Holding and strengthening any position on the Russian-controlled side of the Dnipro river could present a tough challenge for Ukrainian troops.
Boggy, swamp-like terrain makes amphibious landings difficult, and Russia has significant access to manpower and equipment on the eastern side of the river.
- 'Blast wave' -
The claims came as Russia continued to pound southern and eastern Ukraine, in attacks that Kyiv said targeted civilian infrastructure.
Two rescue workers arriving at the scene of a Russian strike in Zaporizhzhia region were killed by a second strike, Interior Minister Igor Klymenko said on social media.
"Rescuers were at the scene in a matter of minutes. Then the occupiers struck again," he said.
The victims were 31 and 34 years old, he added.
It was not immediately clear where or when the attack took place. The region's governor had said earlier that Russia launched three rocket attacks at a town in Zaporizhzhia region Wednesday, killing one person and injuring seven others.
"The blast wave and shrapnel damaged houses, two cars and outbuildings located near the site of the strikes," governor Yuriy Malashko said.
In a separate attack, the interior ministry said overnight Russian shelling of a high-rise building killed two people in the eastern town of Selydove in Donetsk region.
"As of now, there are two dead in Selydove," it said.
The bodies of a 59-year-old local man and an 85-year-old woman had been pulled from the rubble, it added.
In his evening address, Zelensky warned that there are likely more people under the rubble.