US President Donald Trump was accused of "destroying trust" between world leaders in matter of "seconds" after he backed out of the G7 agreement via two angry tweets.
The US leader stunned the world by tearing up the joint statement which leaders and diplomats spent days painstakingly drafting just hours after it had been approved.
He fired off furious tweets saying he told US representatives "not to endorse the Communique" and accusing Canadian Prime Minister Justin Trudeau - who hosted the summit - of being "dishonest and weak".
But French president Emmanuel Macron said "International cooperation cannot be dictated by fits of anger and throwaway remarks".
He added: "We spent two days working out a (joint) statement and commitments. We are sticking to them and whoever reneges on them is showing incoherence and inconsistency.
"Let's be serious and worthy of our people. We make commitments and keep them," Macron's office said, adding that "France and Europe maintain their support for this (G7) statement."
German Foreign Minister Heiko Maas meanwhile slammed the US President over the move and warned it will take some time before trust can be rebuilt.
He also accused Trump of chipping away at his relationship with his Western allies by unilaterally pulling out of the Iran nuclear deal.
Maas said: "It's actually not a real surprise, we have seen this with the climate agreement or the Iran deal.
"In a matter of seconds, you can destroy trust with 280 Twitter characters."
And he warned that it would take much longer to rebuild the lost trust.
The German foreign minister is the first senior Western politician to publicly condemn to President for shock move.
The joint communique is a statement of broad goals and principles endorsed by the G7 leaders, and Trump's refusal means that this will be the first year that the annual summit fails to issue one.
Instead, Canada will likely issue a chair's summary of the meeting listing the major topics of discussion.
Trump slammed Trudeau for "making false statements" and accused him of being "meek and mild" in their one-on-one meeting.
The US leader is at loggerheads with the rest of the G7 over his controversial 25 per cent steel tariffs.
The President insists he has slapped the levies on to hit back at charges imposed by other countries and has accused his allies of trying to milk the Us's economy.
But other G7 leaders have warned that the protectionist tariffs couple plunge the world into a trade war - pushing up prices for consumers in the long term.
The White House initially said that Trump's meeting with Trudeau was "great" and the leaders were "close to a deal" on trade.
But Trump's latest counter-punch cast doubt on any hopes for a quick resolution of his mounting tariff disputes with Canada and the European Union, and signalled that Trump is far from backing down.
After boarding a flight for Singapore, where he will meet North Korea's Kim Jong Un, Trump tweeted: "PM Justin Trudeau of Canada acted so meek and mild during our G7 meetings only to give a news conference after I left saying that, 'US Tariffs were kind of insulting' and he 'will not be pushed around.'
"Very dishonest & weak. Our Tariffs are in response to his of 270% on dairy!"
Trump then tweeted: "Based on Justin's false statements at his news conference, and the fact that Canada is charging massive Tariffs to our US farmers, workers and companies, I have instructed our US Reps not to endorse the Communique as we look at Tariffs on automobiles flooding the U.S. Market!"
Trump was reacting to comments made by Trudeau at a press conference on Saturday in which he threatened to torpedo negotiations on a new NAFTA deal if the Americans did not remove tariffs on Canadian steel and aluminum.
Trudeau said he told Trump directly that Canada "particularly did not take lightly the fact that [the tariffs were] based on a national security reason." The prime minister said in comments reported by CTV: "Canadians are polite, we're reasonable, but we also will not be pushed around."
The Canadian leader's office defended him against Trump's tweets on Saturday, saying that Trudeau said nothing in his G7 news conference that he has not said before directly to Trump
'The prime minister said nothing he hasn't said before — both in public, and in private conversations with the president,' Trudeau's office said in a statement released on Twitter, which added Trudeau remained focused on what was accomplished at the two-day summit in Quebec.
In one behind-the-scenes account from the G7, a French presidential official described an 'extraordinary' session in which leaders surrounded Trump and showered him with data one after the other in an attempt to sway him to drop US tariffs.
Trump gave 'a long, frank rant', the official said, repeating his position that the US had suffered at the hands of its trading partners, as French President Emmanuel Macron tried to push back.
It was a ' long litany of recriminations, somewhat bitter reports that the United States was treated unfairly,' said the French official, who spoke on condition of anonymity. 'It was a difficult time, rough, very frank.'
White House officials did not immediately respond to requests for comment on the characterisations by the official of Trump's remarks.
Trump himself told reporters on Saturday that the summit was not contentious and called his relationship with G7 allies a '10'.
The trade dispute was launched after Trump last week removed exemptions from steel and aluminum tariffs on imports from Canada, Mexico and the EU.
Canada responded by slapping tariffs on $12.8billion worth of US exports, including metals, toilet paper, ball point pens and pizza.
'We're like the piggy bank that everybody is robbing,' Trump said at a press conference as he departed the two-day meeting in La Malbaie, Quebec on Saturday.
'This isn't just G7. I mean, we have India, where some of the tariffs are 100 percent ... And we charge nothing,' Trump said. 'And it's going to stop. Or we'll stop trading with them.'