Trump's comments on Saturday came shortly after Trudeau, who was hosting the G-7 meeting in Canada, had projected an image of cooperation. "We will try to understand the reasoning that have pushed people to take the positions they have and we will act accordingly".

"They understand. They're trying to act like, "Well, we fought with you in the wars" but they don't mention the fact that they have trade barriers against our farmers, they don't mention the fact that they're charging nearly 300-per-cent tariffs".

Responding to Trump, Trudeau's spokesperson Cameron Ahmad said: "We are focused on everything we accomplished here at the G7 summit".

Ontario premier-designate Doug Ford is also among those setting aside his political differences with Trudeau, re-asserting today that he stands "shoulder to shoulder" with the prime minister on trade.

"I highlighted directly to the president that Canadians did not take it lightly that the United States has moved forward with significant tariffs on our steel and aluminum industry", Trudeau said at a news conference at the meeting's end.

"Our national security relationship with Canada is vital and saves American lives".

A few minutes later, Trump changed his Twitter profile header picture from the G7 family photo to a photograph of himself singing the anthem with members of USA military in Atlanta in January this year - apparently another jab at his summit-mates, considering how far back he had to dig to find that one.

President Donald Trump arrives for the G7 Summit, Friday, June 8, 2018, in Canadian Forces Base Bagotville, Canada.

Trump tweeted on his way to Singapore where he is expected to meet with North Korean leader Kim Jong Un and appeared, at least on Twitter, optimistic about the outcome.

"It's economic. It's the balance sheet".

In a message earlier on Friday on Twitter, Trump said the talks at the summit would "mostly center on the long time unfair trade practiced against the United States".

"Trump did not want to be isolated", Macron said.

Ahead of his departure, Trump had criticised his predecessors for negotiating "unfair" trade deals. The member states imposed sanctions. The noise of 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. "Very dishonest and weak", Trump said. Russian Federation no longer remained a part of the summit following its annexation of Crimea back in 2014.

"Russia should be in this meeting. I might have had a very different" response, Trump said.

The president met with leaders from Canada, Britain, Italy, France, Germany and Japan in Quebec, where trade talks dominated the summit.

Trudeau's office said he had not said anything in his closing G7 news conference he has not said to Trump before.

He described Trudeau's actions during the G7 as a "sophomoric play". We have seen this with the climate agreement or the Iran deal.

Trump was reacting to comments made by Trudeau 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.

"It was not contentious", Trump said. "Tariffs will come way down".

The majority of Canadian exports go to the United States, making Canada uniquely vulnerable to a USA trade war.

"It's like the gig is up", he said.

"We strive to reduce tariff barriers, non-tariff barriers and subsidies", it said.

These tariffs, they told Trump, would hurt everyone.

Former FBI director James Comey, who was unceremoniously fired by Trump, tried to strike a reassuring tone on Twitter. They didn't tell you that, did they?

Yet Buthe cautioned: "These kind of things can spiral out of control fairly quickly" as countries hammer each other with escalating retaliatory tariffs.