Rishi Sunak has pledged to "call out Putin's regime" at this year's G20 summit over the devastating turmoil inflicted by Russia's invasion of Ukraine.
But Russian President Vladimir Putin is not expected to attend the gathering, having faced widespread international condemnation over his war with Ukraine.
Foreign minister Sergei Lavrov is instead expected to represent the Kremlin at the event in Bali.
The annual gatherings were initially established in response to the 2008 financial crisis, cementing the summit as the main global forum for economic cooperation.
But Mr Sunak warned this year's summit - the first since the Kremlin sent troops into Ukraine in February - would not be "business as usual".
The meeting will take place as the world faces the most significant set of economic challenges since 2008 - caused or exacerbated by the actions of Russia, a G20 member state.
Talks are set to be dominated by the fallout of the Kremlin's invasion, which has unleashed chaos in the global economy and seen energy and food prices skyrocket.
In a statement ahead of his departure, Mr Sunak said: "Putin's war has caused devastation around the world - destroying lives and plunging the international economy into turmoil.
"This G20 summit will not be business as usual.
"We will call out Putin's regime and lay bare their utter contempt for the kind of international cooperation and respect for sovereignty forums like the G20 represent.
"In clear contrast to Putin's disruption, the UK and our allies will work together to make meaningful progress solving the economic challenges we face and making lives better for our people."
Under pressure to perform both at home and abroad
Mr Sunak - who replaced ill-fated predecessor Liz Truss less than three weeks ago - faces a testing week on both the international stage and at home in the UK, where he is set to unveil his highly anticipated autumn budget on Thursday.
But before that, Mr Sunak will confront Mr Lavrov in a speech during the G20's first plenary session - when all members are expected to attend - on Tuesday.
Russia's top diplomat previously walked out of a meeting of G20 foreign ministers in July when challenged over Moscow's actions in Ukraine.
But reaching an accord on international issues has often proved problematic for the group of 20 major economies - including geopolitical rivals China and the US.
And divisions deepened by the Ukraine war mean it is unclear whether a traditional joint statement will be agreed at the end of the Bali summit.
Organisers in Indonesia are understood to have axed the official "family photo" amid tensions among some leaders over posing alongside the representative for Russia.