After Mr. Trump's departure from the G-7, Mr. Trudeau held a press conference Saturday stating that all of the member nations, including the USA, had signed a communique pledging to lower tariffs and other trade barriers.

Kudlow had been negotiating nicely with Trudeau at the summit in Quebec and the United States had agreed to join the joint communique, but Trump pulled out after he felt betrayed by Trudeau's news conference where the prime minister called Trump's tariffs on Canadian aluminum and steel exports "insulting".

Mr. Trudeau's office responded to Mr. Trump's tweets accusing the Canadian leader of "false statements" on Saturday, saying that the Prime Minister said nothing during the G7 summit that he had not said previously.

"I have instructed our U.S. Reps not to endorse the Communique as we look at Tariffs on automobiles flooding the U.S. Market!", Trump tweeted Saturday evening while en route to Singapore aboard Air Force One.

"Canada will not change its mind when it comes to the illegal and absolutely unjustified application of tariffs on steel and aluminum, not only coming from Canada, but on the steel and aluminum sold by all the G7 allies who are assembled here, to the United States", Freeland said in a news conference at the summit.

It is unclear if Trump's focus on getting tough with trade partners, and solving the North Korean nuclear issue will have some influence on voters in the mid-term congressionsal elections in November. But short of that, he also pledged the US would raise its own trade barriers to combat unfair trade practices around the world.

Mr Kudlow suggested Mr Trump saw Mr Trudeau as trying to weaken his hand before that meeting, saying the president won't "let a Canadian prime minister push him around".

Another US trade adviser, Peter Navarro, said: "There is a special place in Hell for any leader that engages in bad faith diplomacy with President Donald J Trump and then tries to stab him in the back on the way out the door".

Trump said in another tweet that Trudeau was "meek and mild" during their private meeting, only to hold a news conference calling the USA tariffs "insulting".

Germany's Angela Merkel later described Mr Trump's decision to reject the joint communique initially agreed between the G7 leaders as "sobering" and "depressing". As he flew from Canada to Singapore Saturday night, Trump displayed his ire via Twitter, which he also employed to insult Trudeau as "dishonest" and "weak". According to a Canada release, they make nearly 100 Billion Dollars in Trade with US (guess they were bragging and got caught!).

The president's move to reject the communique contradicted a statement from Trudeau earlier, in which the prime minister announced "we have released a joint communique by all seven countries".

As for the comments by Trump's aides, she said, "Canada does not believe that ad hominem attacks are a particularly appropriate or useful way to conduct our relations with other countries".

Europe's answer must be to stick even closer together, defend its interests and strengthen alliances with countries such as Japan and Canada, Mr Maas said.

Kudlow, the conservative economist who directs the National Economic Council, was upset with Trudeau's comments at a press conference after the contentious Group of 7 summit in Quebec.

The group of seven nations that make up the G7 are Canada, France, the U.S., the UK, Germany, Japan and Italy. "The president could have said that. It is impossible to predict what Trump will do next", said a senior G7 official on the summit outcome.

In his news conference, Mr Trudeau had spoken of retaliatory measures that Canada would take next month in response to Mr Trump's decision to slap tariffs on steel and aluminium imports.

The White House did not immediately respond to a request for comment on why Trump had focused his tweets on Canada and the European Union over trade disputes and on North Atlantic Treaty Organisation partners over defense costs and not on his talks with Kim set for Tuesday.

On Sunday, Trudeau ignored the barbs from Trump's advisors, tweeting a link to the G7 communique and hailing the "historic and important agreement we all reached".