Sir Keir Starmer has condemned Russia’s “barbaric” drone and missile attack on Kyiv overnight.
Moscow’s strikes killed at least 18 people in the Ukrainian capital and injured scores more.
The barrage which lasted for 11 hours into Thursday morning hit locations over a wide area of the city, damaging residential buildings and civilian infrastructure.
In a statement, read out by a Downing Street spokeswoman, the Prime Minister said: “I am utterly appalled by Russia’s latest barbaric assault on Kyiv, which has killed and injured innocent civilians.
“These attacks are a stark reminder that while Ukraine continues to pursue peace, (Vladimir) Putin continues to inflict suffering and violence on the Ukrainian people.
“The UK will continue working with allies to increase pressure on Russia and support Ukraine in securing a just and lasting peace. We stand with Ukraine for as long as it takes.”
Authorities in Moscow said the bombardment was in retaliation for Ukraine’s ramped-up strikes on Russian oil refineries that have caused fuel shortages and put pressure on Mr Putin.
The Kremlin insisted its overnight strikes exclusively targeted military-linked sites.
The attack came days before a crucial Nato summit begins in Turkey’s Ankara next Tuesday.
The No 10 spokeswoman appeared to play down suggestions that the timing of Moscow’s strikes was deliberate, saying the Russian president “has proven throughout his barbaric war on Ukraine that he launches attacks indiscriminately”.
More than 16,000 Ukrainian civilians have been killed since Russia launched its full-scale invasion more than four years ago, according to the United Nations.
Tory former prime minister Boris Johnson said western nations must do more to force Mr Putin to the negotiating table.
Responding to Moscow “murdering women and children” in Kyiv, he wrote on X: “Why won’t we systematically take out the shadow fleet? Why won’t we give the Ukrainians the hundreds of billions of frozen assets?
“And why the hell is the UK – of all countries – now buying Russian aviation fuel, even if it has been refined in third countries, under a loophole recently opened by Keir Starmer? This means British cash is helping to fund Putin’s war machine. It’s a total disgrace and if Starmer wants a legacy he should end the practice now.”
Mr Johnson was referring to trade licences issued earlier this year allowing for the import of Russian jet fuel and diesel refined in third countries.
Ministers at the time denied that the move represented a watering down of sanctions aimed at hurting Moscow’s economy, saying the two short-term licences were issued to phase in a new package of sanctions last month.
The Government last month confirmed those licences will expire by January 1, 2027 at the latest.
