President Donald Trump has delivered a further blow to the US relationship with traditional allies by retracting his endorsement for a joint communique with G7 leaders and threatening to escalate a brewing trade war.
The US leader took to Twitter shortly after the summit in Canada ended on Saturday, accusing Canadian Prime Minister Justin Trudeau of dishonesty and withdrawing Washington's endorsement of the statement which vowed to fight protectionism.
Trump recently ignited a trade dispute by imposing tariffs on his North American and European partners' steel and aluminium exports and repeated a threat to impose tariffs on car imports.
At the close of the summit, host Trudeau said the new tariffs on Canada under national security pretexts were "insulting" and that "Canadians are polite and reasonable but we will not be pushed around."
He said retaliatory measures against the US would come into place on July 1, even though it was "not something we want to do".
Canada is the US' second largest trading partner and experts warn jobs on both sides of the border would be affected.
Trump, who left the summit early for his Singapore summit with North Korean leader Kim Jong Un, took umbrage.
"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 US Market!," he tweeted from his plane.
"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 per cent dairy!"
In response, Trudeau's office said the prime minister had "said nothing he hasn't said before - both in public, and in private conversations with the president" while an EU official told dpa the bloc would "stick to the communique as agreed by all participants."
Trump's about-turn also earned him a rebuke from long-time critic, Republican Senator John McCain, who tweeted to US allies, "Americans stand with you, even if our president doesn't."
At his press conference before leaving, Trump had radically suggested the seven nations cut all tariffs and other barriers to trade but also threatened to entirely stop trading with the other nations if they did not end what he described as "unfair trading practices".
The sides had managed to eke out a compromise final summit statement that pledged to protect the international rules-based order and reform the trade system.
Prior to the summit, Donald Tusk, the president of the European Council, had openly expressed concern that the "rules-based international order is being challenged" by the US, long seen as its architect and protector.
"No tariffs, no barriers, that's the way it should be, and no subsidies," Trump told reporters he had proposed to the other leaders, describing the idea as "the ultimate thing."
He insisted, however, that his relationship with the other six leaders was "outstanding" and stressed he blamed his own predecessors in the White House for the current trading system.
"In fact, I congratulate leaders of other countries for so crazily being able to make these trade deals so good for their countries," Trump said. "We're like the piggy bank that everyone is robbing, and that ends."
Trump has repeatedly bashed allies who sell more goods to the US than they buy, though Europeans openly dispute his maths on trade deficits and insist their companies create US jobs.
French President Emmanuel Macron said Europe put up a united front at the summit, also attended by the leaders of Britain, Italy, Germany and Japan.
"Trump did not want to be isolated," Macron said. "We managed to convince Trump that six plus one was feasible and he did not want that."