Ukraine: As the Kremlin prepares to defend the largest city under its control from Ukraine's counteroffensive, the Kremlin is digging in for the "heaviest of battles" in Kherson, a senior Ukrainian official said.

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

"This means that no one is preparing to retreat, on the contrary, the heaviest battle is going to be fought for Kherson," Arestovich said in an online video late Tuesday.

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

Yury Sobolevsky, a member of the ousted pro-Ukrainian Kherson Regional Council, said Russia-installed authorities were putting more pressure on Kherson residents to leave.

In the Mykolaiv region, north and west of the city of Kherson, artillery battles erupted throughout Tuesday, according to a post from Frontline on Telegram's pro-Russian channel Rybar.

In the Ishchenka district north of Kherson, Ukrainian troops tried to consolidate their positions but were forced to return to the front lines, the post said.

A media worker in a remote hamlet near part of the Kherson frontline said residents expected Russian troops to withdraw soon.
With no power or gas and little food or potable water in the area, many residents have fled, abandoning cattle to roam among spent ammunition poking from the soil.

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

President Zelenskiy said Russia's allegation suggested Moscow was planning to use a tactical nuclear weapon and would seek to blame Kyiv.

U.S. 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 U.N. The nuclear watchdog said it was preparing to send inspectors to two unidentified Ukrainian sites at Kyiv's request, both already subject to its inspections.

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.