Western leaders appeared relaxed as they started their three-day G7 summit in Germany, with Boris Johnson joking about the group being "tougher" than Vladimir Putin, while also showing a united front in their response to his Ukraine invasion.
They were meeting to discuss how to secure energy supplies and tackle inflation, and trying to ensure the global coalition working to punish Moscow is not splintered.
Amid speculation about the appetite of some leaders to continue to support Ukraine during a prolonged conflict, Mr Johnson said President Putin must not be allowed to "hack" Russia's neighbour apart with impunity.
He said: "The consequences of what's happening for the world are tough, but the price of backing down, the price of allowing Putin to succeed, to hack off huge parts of Ukraine, to continue with his programme of conquest, that price will be far, far higher and everybody here understands that."
The prime minister, US President Joe Biden, and their counterparts from Canada, France, Germany, Italy and Japan, plus the EU, were spending the first day in both formal and informal settings, including discussing the war's effects on the global economy.
They announced infrastructure plans for developing nations, in a new partnership designed to provide an alternative to Russian and Chinese investment there. The US and fellow G7 members aim to raise a total of $600bn (£490bn) by 2027.
During the traditional group photocall involving the leaders of seven of the world's leading economies, the suited politicians were snapped without their ties, as they appeared to try to convey a more informal atmosphere in the Bavarian Alps.
Earlier, as they met for a roundtable discussion at the castle resort of Schloss Elmau, Mr Johnson joked the group had to show they were "tougher" than Mr Putin.
The prime minister and his Canadian counterpart, Justin Trudeau, discussed the Russian leader's history of being photographed without a shirt.
Mr Johnson questioned whether they should keep their jackets on.
Warming to his theme, he then added "shall we take our clothes off?", suggesting "we all have to show that we're tougher than Putin".
Mr Trudeau joined in, referring to a "bare-chested horseback ride" - as Mr Putin was pictured shirtless riding a horse in 2009.
Mr Johnson then said: "We've got to show our pecs."
During a separate meeting between Mr Biden and German Chancellor Olaf Scholz, who holds the G7′s rotating presidency and is hosting the gathering, the US leader said: "We've got to make sure we have us all staying together."
Mr Scholz replied the "good message" is that "we all made it to stay united, which Putin never expected".
"We have to stay together, because Putin has been counting on, from the beginning, that somehow NATO and the G7 would splinter, but we haven't and we're not going to," Mr Biden replied.
"We can't let this aggression take the form it has and get away with it," added the president.
At the summit, the leaders were set to announce new bans on Russian gold imports - the latest in a series of sanctions aimed at further isolating Russia economically over the war.