Vladimir Putin’s attacks on Ukraine’s power grid are “depraved”, Sir Keir Starmer said.

Russian drone and missile attacks have hit civilian infrastructure, leaving more than a million people without heat and power in freezing temperatures.

The Prime Minister and Volodymyr Zelensky discussed the attacks and the UK’s military support for Ukraine in a call on Thursday.

Downing Street said the leaders “discussed the egregious Russian missile strike in the early hours of this morning, which had deprived more than a million people of heat, light and electricity”.

The Prime Minister described the “systemic attacks on Ukraine’s energy sector” as “depraved”, No 10 said.

Foreign Secretary David Lammy said: “Russian attacks on Ukraine’s energy grid as winter bites demonstrate the depths the Kremlin is willing to plumb in its illegal war.

“Their attempts to break Ukrainian resolve will fail. The UK stands with Ukraine against Russian aggression.”

The Ukrainian president said the strikes were “yet another act of Russian air terror targeting Ukraine’s civilian infrastructure, involving over 90 missiles and nearly 100 drones”.

Amid reports that a fresh consignment of Storm Shadow missiles have been sent to Kyiv by the UK, Mr Zelensky said in his call with Sir Keir “we discussed advancing our defence co-operation and strengthening Ukraine’s long-range capabilities”.

UK authorities will not be drawn into confirming it has given Ukraine permission to use the weapons to strike targets inside Russia.

But chunks of debris from Storm Shadows are reported to have been found in Russia’s Kursk region, which borders Ukraine.

Elsewhere, US President Joe Biden’s administration has urged Ukraine to lower its age of conscription from 25 to 18 to help boost its fighting force.