By Jonathan Landay and Pavel Polityuk
MYKOLAIV, Ukraine (Reuters) - Under pressure in the south of Ukraine, Russia fired missiles and drones into Ukrainian-held Mykolaiv on Sunday, destroying an apartment block in the ship-building city near the front and said the war was trending towards "uncontrolled escalation".
Mykolaiv lies roughly 35 km (22 miles) northwest of the front line to occupied Kherson, the southern region where Russia has ordered 60,000 people to flee a Ukrainian counter offensive "to save your lives" .
Russian Defence Minister Sergei Shoigu, who some Russian nationalists have blamed for Moscow's setbacks since the Feb. 24 invasion, discussed the "rapidly deteriorating situation" in calls with French, British and Turkish counterparts, the ministry said.
He also spoke by phone with U.S. Defense Secretary Lloyd Austin for the second time in three days. The Pentagon's readout of the call said Austin told Shoigu he "rejected any pretext for Russian escalation."
Without providing evidence, Shoigu said Ukraine could escalate by using a "dirty bomb" - conventional explosives laced with radioactive material. Ukraine does not possess nuclear weapons, while Russia has said it could protect Russian territory with its nuclear arsenal.
Ukrainian Foreign Minister Dmytro Kuleba rejected the allegation, calling it "absurd" and "dangerous". He added: "Russians often accuse others of what they plan themselves."
The White House National Security Council also rejected Shoigu's claims. "The world would see through any attempt to use this allegation as a pretext for escalation," a statement from the Council said.
CHANNELS OF COMMUNICATION
In his nightly video message, Ukrainian President Volodymyr Zelenskiy said only Russia was capable of using nuclear weapons in Europe, and Shoigu's "telephone carousel" made matters clear.
"Everyone understands full well," Zelenskiy said. "They understand who is the source of all the dirty things imaginable in this war."
A Russian missile strike on Sunday wiped out the top floor of an apartment block in Mykolaiv, sending shrapnel and debris across a plaza and into neighbouring buildings, smashing windows and cracking walls. Cars were crushed under rubble, Reuters witnessed. No fatalities were recorded.
"After the first blast, I tried to get out, but the door was stuck. After a minute or two, there was a second loud blast. Our door was blown into the corridor," said Oleksandr Mezinov, 50, who was woken from his bed by the blasts.
Ukraine shot down 14 Russian "kamikaze" drones over Mykolaiv overnight, regional governor Vitaliy Kim said on Telegram. The drones are designed to explode on impact and have hammered Ukraine's energy infrastructure this month.
Ukraine says Russia has used Iranian-made Shahed-136 attack drones. Tehran denies supplying the drones to Moscow - an assertion Washington says is untrue.
Kim said Russia also attacked with S-300 missiles, one of which hit the five-storey apartment building.
INTENSIFYING ATTACKS
Ukraine's advances in recent weeks around Kherson and in the country's northeast have been met with intensifying Russian missile and drone attacks on civilian infrastructure, which have destroyed about 40% of Ukraine's power system ahead of winter.
Russian troops have withdrawn from parts of the front in recent weeks and occupation authorities are evacuating civilians deeper into Russian-held territory before an expected battle for Kherson, the regional capital on the west bank of the Dnipro river. Kherson is a gateway to Crimea, which Russia annexed in 2014.
"The situation today is difficult. It's vital to save your lives," Russian Education Minister Sergei Kravtsov said in a video message. "It won't be for long. You will definitely return," he added.
Russia-installed authorities there reported a shortage of vessels to ferry people across the river at one point on Sunday, blaming a "sharp increase in the number of people wishing to leave."
Around 25,000 people have been evacuated since Tuesday, the Interfax news agency said.
Ukraine's military said it was making gains in the south, taking over at least two villages it said Russia had abandoned.
Reuters could not independently verify the accounts.
WINTER MISERY LOOMS
Russia and Ukraine have accused each other of planning to blow up the Nova Kakhovka dam, which holds roughly as much water as the Great Salt Lake in the U.S. state of Utah. Breaching it could flood a swathe of southern Ukraine, including Kherson.
Neither side has produced evidence to back up their claims about the dam, which supplies water to Crimea and the Russian-held Zaporizhzhia nuclear power plant.
Zelenskiy said the Russian attacks on energy infrastructure had struck on a "very wide" scale.
With the war about to start its ninth month and winter approaching, the potential for freezing misery loomed.
More than a million people were without power, presidential adviser Kyrylo Tymoshenko said. A city official said strikes could leave Kyiv without power and heat for days or weeks.
Moscow has acknowledged targeting energy infrastructure but denies targeting civilians in what it calls a "special military operation" in Ukraine.