Lashing out at the longtime US ally and northern neighbour, US President Donald Trump tweeted that Canadian Prime Minister Justin Trudeau is "dishonest & weak".
He tweeted that the US was pulling back its endorsement of the G7 summit's communique in part because of what he called Trudeau's "false statements" at a news conference.
In an extraordinary set of tweets aboard Air Force One, on its way to Singapore for Tuesday's summit with North Korea's Kim Jong Un, Trump threw the G7 summit into disarray and threatened to escalate his trade war just as Canada released the G7's official communique.
Its statement took a generally positive view of the leaders' positions on trade matters while acknowledging tensions with the US.
A few hours earlier, Trudeau had told reporters that all seven leaders had come together to sign the joint declaration.
Trump 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 US Market!"
He followed up by tweeting: "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!"
In a statement, a spokesman for Trudeau did not address Trump's insults.
"We are focused on everything we accomplished here at the #G7 summit," spokesman Cameron Ahmad said. "The Prime Minister said nothing he hasn't said before — both in public, and in private conversations with the President."
Trump's personal attack on Trudeau is unprecedented in the countries' longstanding relationship.