Sir Keir Starmer will seek to step up pressure on Russia with a package of new sanctions as he attends the G7 summit in France.
The Prime Minister is also expected to hold bilateral meetings with India’s Prime Minister Narendra Modi and Ukrainian President Volodymr Zelensky on Tuesday.
The measures, to be announced as the Prime Minister discusses Ukraine with G7 counterparts at the summit in Evian-les-Bains, will target Russia’s shadow fleet and the finance networks the country uses to circumvent western sanctions.
They will also sanction several vessels identified as moving banned Russian liquefied natural gas.
It will bring the number of sanctioned shadow fleet and Russian LNG vessels to more than 600.
They are also expected to target a network involved in covertly procuring western technology for Russia’s military, and third country suppliers helping Moscow move money internationally.
British troops seized a Russian shadow fleet vessel in the Channel for the first time at the weekend.
The captain of the Smyrtos tanker, Ajay Pant, 38, has been charged with contravening sanctions by the Crown Prosecution Service and will appear in court on Tuesday.
Sir Keir said: “Russia’s aggression threatens not just Ukraine, but the security of all Europe.
“That is why the UK is stepping up – choking off the revenues that fuel (Russian President Vladimir) Putin’s war and powering Ukraine through the winters ahead.
“We will stand with Ukraine for as long as it takes and this announcement reinforces that. Putin should roll back his tanks, end his barbaric strikes, and come to the negotiating table.”
Sir Keir is facing his counterparts on the international stage to talk about global threats as pressure is piling on him over long-term funding for the military at home.
And there is potential for friction with US President Donald Trump, who was pictured sitting next to Sir Keir at a working leaders’ dinner on the first night of the summit, amid a strained relationship.
Sir Keir has announced a social media ban for under 16s after Mr Trump’s pro-tech US administration warned against such a move.
And recent interventions from vice president JD Vance and defence secretary Pete Hegseth linked to the murder of student Henry Nowak prompted No 10 to criticise those seeking to “interfere in our democracy”.
The Prime Minister and his wife Lady Victoria Starmer met German Chancellor Friedrich Merz at the summit on Monday.
Sir Keir updated Mr Merz on his social media ban and they talked about the UK’s ambitions to move closer to the EU, a Downing Street spokeswoman said.
Sir Keir and Lady Victoria also met Canadian Prime Minister Mark Carney for a drink and talked about strengthening Euro-Atlantic security and innovative financing solutions for defence.
Canada is spearheading the Defence, Security and Resilience Bank, which aims to help member countries fund defence projects at low cost.
The G7 summit also comes as Mr Trump has clinched a peace deal with Iran which he says will see oil flow freely again through the Strait of Hormuz, the vital shipping route out of the Persian Gulf.
The US President said the Strait would be fully opened on Friday when the deal is signed in Switzerland.
