Russia digging in for 'heaviest of battles' in Kherson: Ukrainian official

• Ukraine says Russians strengthening in strategic province.
• Ukrainians prepare advance on entire frontline.
• 'Serious mistake' if Russia used tactical nuclear weapon: Biden.

NEAR KHERSON FRONTLINE, UKRAINE: Russian 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 from Ukraine's counter-offensive.

Russian forces in the region have been driven back in recent weeks and risk being trapped against 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 are evacuating residents to the east bank, but Oleksiy Arestovych, adviser to Ukrainian President Volodymyr Zelenskiy, said there was no sign that Russian forces 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 to have 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 the Russia-installed authorities were putting increasing pressure on Kherson residents to leave.

"Search and filtration procedures are intensifying as are searches of cars and homes," he wrote on the Telegram messaging app.

Artillery duels

In Mykolaiv region north and west of Kherson city, artillery duels raged throughout Tuesday, according to a post from the frontline on Rybar, a pro-Russian channel on Telegram.

In Ishchenka district north of Kherson, Ukrainian forces tried to consolidate their positions, but were forced back to earlier lines, the post said. It said the Ukrainian military was preparing for an advance along the entire length of the frontline.

A Reuters reporter in a remote hamlet near part of the Kherson frontline said residents hoped Russian forces would soon withdraw.

"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.

'Dirty bomb' allegation

Russia told the UN Security Council on Tuesday that Ukraine is 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 UN 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.

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

Biden later spoke by phone with new British Prime Minister Rishi Sunak, and they agreed on the importance of supporting Ukraine, the White House said in a statement.

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

Ukrainian Foreign Minister Dmytro Kuleba told reporters the inspectors would receive full access, and he called on Moscow to demonstrate the same transparency.

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 repeatedly threatening to use nuclear weapons.