In a phone call, US and Russian officials discussed Russia's growing threat to Ukraine.
Defense Secretary Lloyd J. Austin III spoke with his Russian counterpart on Sunday for the second time in three days, US officials said, in a conversation meant to draw a red line that could potentially provoke Russia to launch a nuclear attack on Ukraine.
The conversation with Russia's defense minister, Sergei K. Shoigu, at 7:30 a.m. Eastern time was meant to explain to the Biden administration why President Vladimir V. Putin is increasing the specter of a nuclear attack on Ukraine, two officials said. With his troops back there, Putin has sought to portray the territory in Ukraine he illegally annexed as part of "Mother Russia", saying any US-backed attack inside the region would be viewed as an attack on the Russian homeland. .
Russia's defense ministry confirmed the two men spoke, saying only that they had discussed the situation in Ukraine. Mr Austin and Mr Shoigu spoke on Friday at the Pentagon's initiation. Prior to that, the two last spoke in May.
A US official said on Sunday that Moscow's switch to Iranian drones, coupled with Putin's growing references to nuclear weapons, meant that a desperate Russia was looking for other tools in its arsenal to use. Putin's troops have faced struggles on the battlefield in Ukraine and there is growing anxiety at home about his military's handling of the war.
Conversation with Mr. Austin was one of the phone calls Mr. Shoigu with other top defense officials on Sunday. In talks with his British, French and Turkish counterparts, Shoigu raised concerns about the possibility that Ukraine would use a "dirty bomb", according to the Russian Defense Ministry. Russia has publicly provided no evidence to back up its claims, and the allegations have received a swift and fierce response from Ukrainian and Western officials. Ukraine's foreign minister, Dmytro Kuleba, called them "lies" that were "absurd and dangerous."
"We don't own a 'dirty bomb', or plan to acquire one," he wrote on Twitter.
A so-called dirty bomb would use traditional explosives to spray radioactive material, and Russia had previously warned of the possibility that one could be featured in the Ukraine war.
The White House called Shoigu's claims "totally false," while the Pentagon said Austin "rejects any pretext for Russia's escalation."
Britain's defense ministry also denied the claims.
President Biden has so far gone to great lengths to avoid escalating the nuclear gulf, and has indicated that he still has no plans to directly engage American forces — or U.S. nuclear arsenals — in a war with Russia. At the same time, American officials say the United States will find it difficult not to respond in some way if Putin uses nuclear weapons in the Ukraine war.
Ukrainian President Volodymyr Zelensky has urged more support from the West in light of Putin's nuclear threat.
"When a terrorist state raises the stakes, they definitely feel it won't work," he said in his evening address.
The Russian offensive is seen as an attempt to expand Ukraine's resources.
ZAPORIZHZHIA, Ukraine — Cruise missiles and drones struck again deep into Ukrainian territory, continuing Russia's intense campaign to undermine Ukraine's energy supplies across the country as its troops also hit targets with rocket and artillery fire along the front lines.
With winter weather approaching, Russia and Ukraine are locked in intense firefights across the front in an increasingly urgent attempt to gain big or small while they can. Russia's new offensive has been seen as part of Moscow's efforts to expand pressure across the country to expand Ukraine's defense capabilities and resources.
Even as Ukrainian military authorities show signs that Russian troops have begun moving military equipment out of the southern city of Kherson, where their position is becoming increasingly weak, Moscow has maintained an aggressive stance in the eastern Donetsk region and stepped up artillery strikes in the north. Ukraine.
Russian troops carried out a joint attack in the towns of Bakhmut and Avdiivka in the Donetsk region, the Ukrainian military command announced late Saturday. The two cities have long been at the center of fighting as Russia seeks to expand its control of Donetsk, with Ukrainian forces putting up a steady fight.
In the south, both sides had attacked far behind their respective lines, but the battle had not moved in the past few days. In the north, Ukrainian officials said Russia fired several rockets and mortar rounds on Saturday at at least six settlements in the Sumy region, from which Russia withdrew in April and which has largely avoided attacks since.
Ukrainian officials also reported attacks on Russian targets. The mayor of Ukraine's Enerhodar, an occupied town near the Russian-controlled Zaporizhzhia nuclear power plant, reported the attack on a hotel in the city early Sunday.
"It's loud again in Enerhodar," the mayor, Dmytro Orlov, said in a post on messaging app Telegram alongside a photo of the burning building.
Orlov said he could not confirm whether there were casualties in the attack but added that it was known that Russian and Ukrainian officials working with Russia were using the hotel.
It is impossible to independently verify the reports, but part of Ukraine's campaign against Russian forces has targeted military positions and command headquarters in Russian-controlled territory to force a retreat.
Russian rocket and artillery fire killed eight people and injured 19 on Saturday, Ukrainian officials reported. Two people were killed in the attack in the Zaporizhzhia region and six in the attack in the Donetsk region. Russia launched a wide-ranging attack on power plants and heating stations in what Ukraine described as some of the heaviest attacks in weeks.
"The geography of this new massive attack is vast," President Volodymyr Zelensky said in his evening address on Saturday.
He told Ukraine that Russia was targeting Ukraine's energy supply due to land loss on the battlefield and he urged Ukraine to use electricity sparingly and be prepared for power cuts.
"Our defense forces have everything they need to defend the country and push forward every day," the president said, "I stress: every day."