The Prime Minister said he and European allies spoke to Ukrainian President Volodymyr Zelensky and Donald Trump on Friday to begin “closely aligning” a response to Russia’s “unacceptable” position in Ukraine peace talks.
Sir Keir Starmer, Mr Zelensky and the leaders of France, Germany and Poland held a phone call with the US president to discuss “developments” in the negotiations on Friday, he said.
It came as Ukrainian and Russian negotiators met face to face for the first time since Moscow’s invasion.
The talks in Istanbul lasted less than two hours and the sides agreed to the biggest prisoner exchange since the start of the war in 2022.
Sir Keir said the prisoner swap was “obviously a good thing” but that “we need to be really clear in putting the pressure on for a ceasefire”.
After the phone call, he told reporters in Tirana, Albania: “We just had a meeting with President Zelensky and then a phone call with President Trump to discuss the developments in the negotiations today.
“And the Russian position is clearly unacceptable, and not for the first time.
“So as a result of that meeting with President Zelensky and that call with President Trump we are now closely aligning our responses and will continue to do so.”
More than 40 leaders were at the European Political Community Summit in the Albanian capital for talks expected to focus on intensifying sanctions on Russia if the Kremlin does not agree to a ceasefire, with Russian energy likely to be a target.
Moscow has so far resisted calls for an unconditional 30-day ceasefire backed by both Kyiv and Washington.
Russian President Vladimir Putin did not turn up for talks with Ukraine this week, sending a low-level delegation instead.
The head of Russia’s delegation, Vladimir Medinsky, said the countries had agreed to exchange 1,000 prisoners of war each and that Moscow and Kyiv agreed to provide each other with detailed proposals for a ceasefire.
He said Ukraine had requested a meeting between heads of state, which Russia would consider.
Sir Keir said: “The prisoner swap is obviously a good thing that’s been agreed today, and the fact that talks continue, but I think we need to be really clear in putting the pressure on for a ceasefire.
“And I’m very keen to continue to put that pressure on, because we need to make sure that Putin comes to the table, but his actions this week still show me that he’s not serious yet about peace.”
Also in Tirana, Nato secretary general Mark Rutte told reporters Mr Putin had made “a big mistake” by sending a low-level delegation to Istanbul.
He said: “Ukraine clearly wants to play ball.
“They are very serious about this.”
Sir Keir met European Commission president Ursula von der Leyen on the margins of the event ahead of the UK-EU summit in London on Monday.
Reports suggest a deal on British access to a major EU defence fund could be on the table on Monday, but arguments over fishing rights and a youth mobility scheme may provide stumbling blocks to an agreement.
Kaja Kallas, the EU’s high representative for foreign affairs, said work was progressing on a defence deal, but added: “We’re not there yet.”
Sir Keir has repeatedly declined to give a “running commentary” on the talks or engage in what he described as “megaphone diplomacy” with the EU.
But he said on Friday he was “positive going into Monday”.
