Russia's attacks on Ukraine's energy sector on Monday night, as temperatures dropped to -20C (-4F), were 'barbaric' and 'particularly depraved,' UK Prime Minister Sir Keir Starmer has said.

He made the comments after speaking to US President Donald Trump just hours after Russia struck power plants and critical infrastructure in the capital, Kyiv, and beyond.

The attacks followed a week-long pause that Trump had requested from Russia's President Vladimir Putin during a fierce cold snap in Ukraine.

Trump said on Tuesday that Putin had 'kept his word' and expressed a desire for him to end the war. Top US envoys are scheduled to meet with negotiators from Russia and Ukraine in Abu Dhabi on Wednesday and Thursday.

When asked if he felt disappointed by Russia's renewed attacks, Trump remarked, 'it [the agreement] was on Sunday, and he [Putin] went from Sunday to Sunday. It's a lot, you know, one week; we’ll take anything, because it's really, really cold over there.'

The damage from the strikes was extensive, with more than 1,000 tower blocks in Kyiv without heating and a power plant in the eastern city of Kharkiv rendered beyond repair. Residents were forced to seek shelter in metro stations, with some even setting up tents on the platforms to shield against the freezing temperatures.

In response, authorities have been establishing warming centres across Kyiv and seeking additional generators to manage prolonged blackout scenarios while engineers work to repair the damage. Ukraine has repeatedly expressed a pressing need for more missile supplies from allies.

NATO Secretary-General Mark Rutte was in Kyiv shortly after the attacks, urging member countries to 'dig deep in their stockpiles' to provide the missiles Ukraine urgently requires.

Despite ongoing discussions, President Trump has been striving to end the conflict, though Putin has refused calls for a ceasefire. US envoys Steve Witkoff and Jared Kushner are actively engaging with Russian and Ukrainian negotiators to work through the US-proposed peace deal. A key sticking point involves Russian demands for Ukraine to cede additional territory in the eastern industrial region of Donbas, with Russia making slow progress in that area.

The full-scale invasion of Ukraine commenced in February 2022, causing an extensive ongoing humanitarian crisis.