The United States and Canada have swung sharply towards a diplomatic and trade crisis as top White House advisers lashed out at Canadian Prime Minister Justin Trudeau a day after US President Donald Trump called him "very dishonest and weak".

Key points: Donald Trump announced on Twitter that he was backing out of the joint communique

Donald Trump announced on Twitter that he was backing out of the joint communique Mr Trump said he might double down on import tariffs by hitting the sensitive auto industry

Mr Trump said he might double down on import tariffs by hitting the sensitive auto industry Larry Kudlow accused Justin Trudeau of betraying Mr Trump with "polarising" statements on trade policy

The spat drew in Germany and France, who sharply criticised Mr Trump's decision to abruptly withdraw his support for a Group of Seven communique hammered out at a Canadian summit on Saturday (local time), accusing him of destroying trust and acting inconsistently.

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Canadian Foreign Minister Chrystia Freeland responded to the White House assault by saying ad hominem attacks were not helpful, that Canada would retaliate to US tariffs in a measured and reciprocal way and that Canada would always be willing to talk.

"Canada does not conduct its diplomacy through ad hominem attacks … and we refrain particularly from ad hominem attacks when it comes from a close ally," Ms Freeland told reporters in Quebec City.

Mr Trump's looming summit with North Korean leader Kim Jong-un heightened tension, and White House economic adviser Larry Kudlow accused Mr Trudeau of betraying Mr Trump with "polarising" statements on trade policy that risked making the US leader look weak on the eve of the historic North Korea summit.

Hours after Mr Trump withdrew his support for the joint statement and attacked Mr Trudeau, Mr Kudlow and trade adviser Peter Navarro drove the message home on Sunday morning news shows in an extraordinary assault on a close US ally and neighbour.

"[Mr Trudeau] really kind of stabbed us in the back," Mr Kudlow, the director of the National Economic Council who had accompanied Mr Trump to the summit of wealthy nations on Saturday, said on CNN's State of the Union.

Mr Navarro told Fox News: "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 and that's what bad-faith Justin Trudeau did with that stunt press conference, that's what weak, dishonest Justin Trudeau did."

Donald Trump repeated a list of grievances about US trade. ( Reuters: Leah Millis )

Mr Trump continued the feud on Monday, taking to Twitter say: "Fair Trade is now to be called Fool Trade if it is not Reciprocal.

"Why should I, as President of the United States, allow countries to continue to make Massive Trade Surpluses, as they have for decades, while our Farmers, Workers & Taxpayers have such a big and unfair price to pay? Not fair to the PEOPLE of America!"

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He also linked the issue to what he views as the United States' disproportionate financial contribution to international peace keeping.

"The US pays close to the entire cost of NATO — protecting many of these same countries that rip us off on Trade (they pay only a fraction of the cost-and laugh!)" Mr Trump tweeted.

"The European Union had a $151 Billion Surplus–should pay much more for Military!

"Germany pays 1% (slowly) of GDP towards NATO, while we pay 4% of a MUCH larger GDP. Does anybody believe that makes sense?

"We protect Europe (which is good) at great financial loss, and then get unfairly clobbered on Trade. Change is coming!"

Mr Trudeau did not immediately respond, but his office said on Saturday after Mr Trump withdrew support for the communique that the Prime Minister had not said anything in his closing news conference he has not said to Mr Trump before.

G7 allies seemed as perplexed as Canada at the sudden diplomatic row, and Germany and France accused Mr Trump of destroying trust and acting inconsistently.

Having left the G7 summit in Canada early, Mr Trump's announcement on Twitter that he was backing out of the joint communique torpedoed what appeared to be a fragile consensus on a trade dispute between Washington and its top allies.

Mr Trump also said he might double down on import tariffs by hitting the sensitive auto industry, throwing the G7's efforts to show a united front into disarray.

"In a matter of seconds, you can destroy trust with 280 Twitter characters," German Foreign Minister Heiko Maas said when asked about Mr Trump's U-turn, adding it would take much longer to rebuild lost trust.

Sorry, this video has expired Trump adviser says Trudeau stabbed him in the back

France is also standing by the G7 communique, a French presidency official said, adding anyone departing from the commitments made at the summit would be showing their "incoherence and inconsistency".

"International cooperation cannot depend on being angry and on sound bites. Let's be serious," the French official, speaking on condition of anonymity, added.

Mr Trump has infuriated the European Union, Canada and Mexico by imposing tariffs on steel and aluminium imports.

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.

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.

"Canadians are polite, we're reasonable, but we also will not be pushed around," Mr Trudeau said.

Sorry, this video has expired Donald Trump tells G7 leaders the US wants an end to trade practices he says have led to an exodus of companies from America. (Photo: Instagram/Angela Merkel)

Reuters