Ukraine said on Monday that Russia was preparing for a fresh wave of missiles attacks on its energy grid that have plunged swathes of the country into the cold and dark.
A Ukraine military spokesman said a Russian warship capable of firing cruise missiles had recently deployed to the Black Sea with Kalibr-type missiles on board.
"This indicates that preparations were underway," said spokeswoman Natalia Gumeniuk.
"It's quite likely that the beginning of the week will be marked by such an attack," she added.
With temperatures dipping below zero, repeated Russian attacks have left Ukraine's energy grid teetering on the brink of collapse, and disrupted power and water supplies to millions over recent weeks.
President Volodymyr Zelensky cautioned in an address to Ukrainians late on Sunday that Russia was preparing new aerial attacks.
Moscow's forces would continue the campaign of systematic attacks "for as long as they have missiles", he said.
Zelensky added that the military was preparing itself, alongside Western allies, who have been delivering new air defence systems to Ukraine.
Russia has said it only targets military-linked infrastructural facilities and blamed the blackouts and their civilian impact on Kyiv's refusal to negotiate with Moscow, not on Russian missile attacks.