R ussian forces are digging in for the "heaviest of battles" in the strategic southern region of Kherson, a senior Ukrainian official said, as the Kremlin prepares to defend the largest city under its control in Ukraine.

Russian forces in the region have been driven back in recent weeks and risk being trapped on the west bank of the Dnipro River, where the provincial capital of Kherson has been in Russian hands since the early days of the invasion of Ukraine eight months ago.

Russian-installed authorities have been encouraging residents to flee to the east bank, but Oleksiy Arestovych, adviser to Ukrainian President Volodymyr Zelenskiy, said there was no sign that Russian forces themselves were preparing to abandon the city.

"With Kherson everything is clear. The Russians are replenishing, strengthening their grouping there," Arestovych said in an online video late on Tuesday.

"It means that nobody is preparing to withdraw. On the contrary, the heaviest of battles is going to take place for Kherson."

Of the four provinces Russian President Vladimir Putin proclaimed annexed in September, Kherson is arguably the most strategically important. It controls both the only land route to the Crimea peninsula Russia seized in 2014 and the mouth of the Dnipro, the vast river that bisects Ukraine.

Yuri Sobolevsky, a member of the ousted pro-Ukrainian Kherson regional council, said Russia-installed authorities were putting increasing pressure on Kherson residents to leave the city and head towards Russia.

"Search and filtration procedures are intensifying as are searches of cars and homes," he wrote on the Telegram messaging app, referring to the questioning and detention of people by Russian forces before some are taken further into Russian-held territory.

Russia says it is evacuating people for their own safety.


A Reuters reporter in a remote hamlet near part of the Kherson frontline heard no shooting or artillery fire on Tuesday. Residents said they hoped Russian forces would soon withdraw from Kherson.

"You fall asleep at night and you don't know if you will wake up," said Mikola Nizinets, 39, referring to Russian shelling.

With no power or gas and little food or potable water in the area, many residents have fled, abandoning cattle to roam among expended munitions poking from the soil.

In the northeast, Russian forces continued to try to seize the town of Bakhmut, which sits on a main road leading to the cities of Sloviansk and Kramatorsk in the Donetsk region, Ukraine's General Staff said on Wednesday.


Russia told the U.N. Security Council on Tuesday that Ukraine was preparing to use a "dirty bomb", an assertion dismissed by Western and Ukrainian officials as a false pretext for intensifying the war.

Russia's Deputy U.N. Ambassador Dmitry Polyanskiy said the evidence had been shared with Western counterparts.

"I don't mind people saying that Russia is crying wolf if this doesn't happen because this is a terrible, terrible disaster that threatens potentially the whole of the Earth," he told reporters.

President Zelenskiy said Russia's allegation suggested Moscow was planning to use a tactical nuclear weapon and would seek to blame Kyiv, a charge Moscow has dismissed as not being serious.

U.S. President Joe Biden said Russia would be "making an incredibly serious mistake" if it used a tactical nuclear weapon.

In an apparent response to Moscow's allegation, the U.N. nuclear watchdog said it was preparing to send inspectors to two unidentified Ukrainian sites at Kyiv's request, both already subject to its inspections.

Russia's state news agency RIA has identified what it said were the two sites involved - the Eastern Mineral Enrichment Plant in the central Dnipropetrovsk region and the Institute for Nuclear Research in Kyiv.

Since Russian forces suffered major defeats in September, Putin has doubled down, calling up hundreds of thousands of reservists, announcing the annexation of occupied territory, and engaging in nuclear sabre-rattling.

(Reporting by Reuters bureaux; Writing by Grant McCool and Stephen Coates and Andrew Osborn; Editing by Philippa Fletcher)