Volodymyr Zelensky is expected to join the G7 summit in Hiroshima in person as Rishi Sunak and allies seek to turn up the pressure on Russia.
The Ukrainian president will attend the summit in Japan on Sunday, it is understood, as the Prime Minister warned Vladimir Putin “we’re not going away”.
It will potentially bring Mr Zelensky into contact with India’s Narendra Modi and Brazil’s Luiz Inacio Lula da Silva, who have not opposed the invasion like their western allies.
But it would be an opportunity for him to build stronger links with the Indian prime minister, who has remained neutral, and the Brazilian president, who the US has accused of “parroting” Russia propaganda.
Attending G7 – the group that Russia was expelled from over its 2014 annexation of Crimea – would also be a new display of solidarity.
Earlier, Mr Sunak announced Britain is banning Russian diamonds in a new wave of sanctions to pressure Russia that will also prohibit imports of Russian-origin copper, aluminium and nickel.
There has been uncertainty whether the EU will go as far as Britain on diamonds, with the trade particularly lucrative for Belgium, but Mr Sunak said he is “hopeful and confident” allies will follow.
Talks between G7 allies, including US President Joe Biden and France’s Emmanuel Macron, will centre on military and economic support for Ukraine as they seek to show a united front.
Mr Sunak told Sky: “Russia needs to know that we and other countries remain steadfast in our resolve to support Ukraine, not just in the here and now with the resources it needs to protect itself, but for the long term as well.”
He added to ITV News: “They can’t just outlast us in this conflict.
“One of the common topics of conversation I’ll be having and have been having with my fellow leaders is about the longer-term security agreements that we put in place in Ukraine, to deter future Russian aggression.”
The diamond export industry was worth more than £3 billion to Russia in 2021 but No 10 conceded direct imports have been low since the UK sanctioned state-owned miners Alrosa last year.
Britain’s move will add pressure on any hesitant allies to follow suit.
Mr Sunak told the BBC: “I’m hopeful and confident that our partner countries will follow as they have done when we’ve done this previously, that will make the sanctions more effective, ensure that Russia pays a price for its illegal activity.”
Mr Sunak’s official spokesman said: “Guarding against economic coercion is something that the Prime Minister is pushing for.”
On Sunday, Mr Sunak told reporters travelling with him in Japan that he has seen “positive” steps from India but that they needed to keep the dialogue open with Mr Modi and Mr da Silva.
“One thing we have to keep doing is talking to countries like India and also Brazil, that is going to be in that second part of the summit which is a good thing,” the Prime Minister said.
India is being represented at the G7 summit because it is the current G20 chair, while Brazil has been invited as a guest.