PM SIR Keir Starmer was locked in talks with US President Joe Biden last night over letting Ukraine attack Russia with British missiles.
Their White House summit came as Russia kicked out six British diplomats.
The Foreign Office said the expulsions over spying allegations were “completely baseless”, as tensions heightened.
Ukraine President Volodymyr Zelensky yesterday put pressure on the West to unleash its firepower, saying: “There should be no unanswered questions about why Ukraine needs sufficient long-range capabilities.”
His pleas came after the PM publicly backed Ukraine’s right to defend itself despite the warning from Vladimir Putin that Russia would be at war with Nato if British Storm Shadow missiles were unleashed against his country.
Mr Biden is widely seen as the last block on freeing Ukraine to strike Russia.
Read More on Politics
In his statement, Mr Zelensky said: “When we ask for these systems, we repeatedly hear, ‘We are working on it’.
“Time passes, but Russian missiles and Iranian drones continue to terrorise our skies and our people.
“Our soldiers are showing incredible heroism, but they need reinforcements.
“These reinforcements mean equipped, ready-to-fight units in sufficient numbers to not only hold ground but regain it.
Most read in The Sun
“We have been asking for this from our partners for months.
“I am grateful to those who made commitments and are fulfilling them but we are still far from fully implementing what has been agreed.
“It’s difficult to repeatedly hear, ‘We are working on this,’ while Putin continues to burn down our cities and villages.”
Foreign Secretary David Lammy and US Secretary of State Antony Blinken were pressed on the use of Western weaponry during their visit to Ukraine earlier this week but said they had to report back to their bosses.
On Thursday, Sir Keir said the UK did not “seek any conflict with Russia”, before adding: “That’s not our intention.”
Mr Putin said allowing long-range strikes “would mean that Nato countries, the United States, and European countries are at war with Russia”.
Last night, ex-PM Boris Johnson met Mr Zelensky in Kyiv and said: “It is vital Ukraine be able to defend itself properly by stopping the appalling Russian attacks with glide bombs and now Iranian missiles.
“It is obvious that they should be able to use Storm Shadow, Scalp and ATACMS as fast as possible.”