The Ukrainian military has warned that Russia is preparing for a new wave of missile attacks against its energy grid.
Natalia Gumeniuk, a spokeswoman for the Ukrainian military, said a Russian warship carrying Kalibr-type missiles had recently deployed to the Black Sea.
"This indicates that preparations were underway," she said.
"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.
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.
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. The spokesman said the deployment was part of a "growing Russian military presence" in the region and called on Russia to "de-escalate the situation."