Trump was reacting to Canadian Prime Minister Justin Trudeau, who said Saturday that Canada would retaliate for Trump's proposed new tariffs.

Trudeau did not respond to the USA attacks, instead declaring the summit a success.

Trump reacted swiftly onboard Air Force One as it traveled to Singapore for the historic U.S.

Saying Trudeau is "dishonest & weak", he also threatened "tariffs on automobiles flooding the U.S. Market!" He also said that because of Trudeau's comments, he instructed US trade representatives to not sign the communique the G-7 leaders had agreed upon expressing the need for "free, fair, and mutually beneficial trade".

White House economic adviser Larry Kudlow accused the Canadian PM of betraying Mr Trump with "polarising" statements on trade policy that risked making the U.S. leader look weak ahead of a historic summit with North Korean leader Kim Jong Un.

In a tense interview today with CNN's Jake Tapper on "State of the Union", Trump's economic advisor Larry Kudlow lambasted Trudeau.

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

"He held a press conference and he said the insulting".

This allegedly unfair playing field, Mr Trump contended, meant that Canada found itself in a competitive advantage across industries as varied as dairy, lumber and energy.

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"We are convinced that a modernisation is perfectly possible, we are convinced that common sense will triumph", she said.

On Saturday, Trump repeated his desire to have a sunset clause in an updated NAFTA deal, a demand Trudeau rejected again.

White House economic adviser Larry Kudlow accused Trudeau of betraying Trump with "polarising" statements on trade policy that risked making the USA leader look weak ahead of the historic summit with Kim.

Trump's feud with Trudeau actually started one day before the G7 Summit when Trump took to Twitter to call out Trudeau and French Prime Minister Emmanuel Macron but hit peak-crazy after Trump left the G7 Summit and headed off to Singapore. He had other things, bigger things, on his plate in Singapore. He did him a favor and he was even willing to sign that socialist communique. Macron said Thursday on Twitter, "The American President may not mind being isolated, but neither do we mind signing a 6 country agreement if need be".

Last year, the U.S. president was wowed by a French military parade in Paris after being invited to join Mr Macron for his country's annual Bastille Day celebrations. "That will not stand", he noted.

Trump's team kept up the barrage of criticism on United States media Sunday. The negotiators included agree-to-disagree language on climate change and on an global commitment to reduce plastics in the world.

Those tensions boiled over on Saturday, with Trudeau and European leaders reaffirming plans to institute retaliatory measures and Trump lashing out in response by refusing to endorse the the G7 communique, a negotiated statement on shared priorities among the group.

Fielding questions from reporters, Mr Trudeau reiterated the United States tariffs were unjust, his Government planned to go ahead with retaliatory measures, and that he had told Mr Trump as much. "$800 billion trade deficit", he said. The measure hits European Union trading partners even though the main target is overcapacity at state-backed Chinese producers, who Europe and the US have long complained have flooded markets with cheap steel. However, the USA was still way ahead of the others, donating 3.57 percent of its GDP, while European countries paid up 1.46 of GDP on average, with Canada lagging behind at 1.29 percent. "But we say that with great sadness".