Rishi Sunak has warned Russia’s allies they are “on the wrong side of history”.
The prime minister is at a major international summit on Ukraine in Switzerland where he will meet Volodymyr Zelensky.
It comes after Mr Sunak said G7 leaders had reached a “historic breakthrough” at a summit in Italy this week by agreeing a loan for Ukraine that will be funded by frozen Russian assets in Europe.
He said: “This is just and it is right. But true justice will only come when Russia leaves Ukraine.”
US vice-president Kamala Harris, French president Emmanuel Macron and the leaders of Germany, Italy, Canada and Japan are among those attending the meeting at the Buergenstock Resort on a cliff overlooking Lake Lucerne this weekend.
The presidents of Ecuador, Ivory Coast, Kenya and Somalia will also join the summit, where Mr Zelensky predicted “history being made”.
Russia was not invited to the talks, while China – its most important ally – has refused to attend.
With Russia holding no invitation, experts and critics do not expect any major breakthroughs for Ukraine. Russian president Vladimir Putin suggested the summit is “just another ploy to divert everyone’s attention”.
As for Mr Sunak, he will criticise countries supplying arms and components for Mr Putin’s war effort.
He will say: “Those who aid Russia by providing the weapons of war, or components for those weapons should look at this summit today.
“They should look at Bucha, Mariupol, Kharkiv, and they should reflect on the choice they have made.
“They are placing themselves on the side of the aggressor – and on the wrong side of history. Putin has no interest in a genuine peace.
“He has launched a sustained diplomatic campaign against this summit, ordering countries to stay away, spinning a phoney narrative about his willingness to negotiate.
“We should ask Russia why they feel so threatened by a summit discussing the basic principles of territorial integrity, food security and nuclear safety.”
Mr Sunak will add: “From a position of strength, we must work with President Zelensky to set out the principles for a just and lasting peace, based on international law and the UN Charter.
“That is the path to a permanent cessation of hostilities. It will show Ukraine that we’ll stand by them when they are ready for negotiations.
“And it will show Putin’s allies in North Korea, Iran and elsewhere that we will protect the right of all nations to determine their own future.”
Additional reporting by Press Association
Emily Foster is a globe-trotting journalist based in the UK. Her articles offer readers a global perspective on international events, exploring complex geopolitical issues and providing a nuanced view of the world’s most pressing challenges.
