Kyiv residents huddled against bitter winter cold inside their unheated apartments on Saturday as engineers struggled to restore power, water and heat knocked out in the latest salvo of Russian strikes.

Four people were killed and 25 others injured in Kyiv after Russia launched a mass attack across Ukraine overnight on Jan. 8-9. Rescue workers were among the victims of Russia's double-tap strike.

Russia has carried out some of the heaviest attacks on Kyiv in months, using an estimated 500 drones and 40 missiles, said Ukrainian President Volodymyr Zelenskyy.

Russia has attacked two foreign-flagged civilian vessels with drones in the southern Odesa region, killing a Syrian national and injuring another, Ukrainian officials said on Friday.

UK Defence Secretary John Healey, who is on a visit to Kyiv, and his Ukrainian counterpart Denys Shmyhal have signed a roadmap to implement the 100-year defence partnership agreement previously signed by the two countries.

"Emergency power cuts have been introduced in Kyiv due to the consequences of shelling and network overload. Emergency power cuts are not subject to schedules, as they occur in response to critical imbalances in the power system," the statement said.

Kyiv's electricity system, severely damaged by a winter campaign of Russian bombardment including a strike two nights ago, has been turned off for repairs at the orders of the state grid operator, the city administration said on Saturday amid intense cold weather.

The first seven "invincibility carriages" have opened in Kyiv Oblast in response to the large-scale power outages caused by recent Russian attacks. [An invincibility carriage is a heated stationary train carriage to help those affected by power cuts – ed.