US President Donald Trump has retracted his endorsement of the joint communique issued at the end of the G7 summit, accusing Canada of "dishonesty".
He said that other countries were imposing "massive tariffs" on the US.
The joint communique, advocating a "rules-based trading system", was reached despite tension over US tariffs on steel and aluminium imports.
Canadian Prime Minister Justin Trudeau vowed afterwards to press ahead with retaliatory tariffs on 1 July.
Speaking at a news conference, he described as "insulting" Mr Trump's decision to invoke national security concerns to justify steel and aluminium tariffs.
"It would be with regret but it would be with absolute clarity and firmness that we move forward with retaliatory measures on 1 July," Mr Trudeau said. "Canadians are polite and reasonable but we will also not be pushed around."
His words contained nothing he had not said before, both in public and in private conversations with Mr Trump, his office said later.
The EU said it would stick to the joint communique despite Mr Trump's decision.
"We stand by the commitments made in the G7 communique," a senior UK government source said.
A French presidential official described the Friday session as "extraordinary", saying leaders who had vowed to confront Mr Trump over his decision to impose tariffs on US allies last week as part of his "America First" agenda, showered Mr Trump with data one after the other.
Mr Trump gave "a long, frank rant", the official said, repeating a position he carried through the 2016 US election campaign into the White House that the United States had suffered at the hands of its trading partners, with French President Emmanuel Macron pushing back on the assertion and Japanese Prime Minister Shinzo Abe chiming in.
It was a "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."
The US president did not appear to be listening during some of the trade presentations, another G7 official familiar with the meeting said.
White House officials did not immediately respond to requests for comment on the characterizations by these officials of Mr Trump's remarks or attention to the presentations.
Trump himself told reporters on Saturday that the summit was not contentious and called his relationship with G7 allies a "10".
Despite smiles and jokes for the cameras, the tension among the leaders was clear. At one point, German Chancellor Angela Merkel was seen having a brief, intense one-sided conversation with a stony-faced Trump on Friday.
On Saturday, Canadian Prime Minister Justin Trudeau sniped about "stragglers" after Mr Trump was late to a breakfast session on gender equality. Mr Trump left the summit early for Singapore, where he will meet North Korean leader Kim Jong Un next week.
One scene at the very beginning of the gathering of presidents and prime ministers of the biggest industrialized nations set the mood for facing the brash Mr Trump.
He arrived at La Malbaie, the scenic luxury resort on the banks of the St. Lawrence River in Quebec, as the four European leaders and the two EU heads were huddled together in a room to coordinate their strategy. The noise of Mr Trump's helicopter landing was so loud they had to stop talking for a while, in a scene one official compared to the opening from the US television series M.A.S.H.
"The EU understands that the only way with Trump is strength," said one European official. "If you give in now, he will come back tomorrow for more."
'Do not endorse'
Tweeting en route to his next summit in Singapore, Mr Trump said he had instructed US officials "not to endorse the communique as we look at tariffs on automobiles".
He said the move was based on Mr Trudeau's "false statements at his news conference, and the fact that Canada is charging massive tariffs to our US farmers, workers and companies".
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!— Donald J. Trump (@realDonaldTrump) June 9, 2018
He suggested Mr Trudeau was "very dishonest and weak".
Mr Trump had earlier signed the joint statement agreed by all the G7 nations despite the trade row.
He also tweeted defiantly about not allowing "other countries to impose massive tariffs and trade barriers on its farmers, workers and companies".
- REUTERS / BBC