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 President Donald Trump called him "very dishonest and weak".
The spat drew in Germany and France, who sharply criticised Trump's decision to abruptly withdraw his support for a Group of Seven communique hammered out at a Canadian summit on Saturday, accusing him of destroying trust and acting inconsistently.
Canadian Foreign Minister Chrystia Freeland responded to the White House comments by saying that Canada will retaliate to US tariffs in a measured and reciprocal way and that Canada will 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," Freeland told reporters in Quebec City on Sunday.
White House economic adviser Larry Kudlow accused Trudeau of betraying Trump with "polarising" statements on trade policy that risked making the US leader look weak ahead of a historic summit with North Korean leader Kim Jong Un.
Hours after Trump withdrew his support for the joint statement and attacked Trudeau, 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.
"(Trudeau) really kind of stabbed us in the back," Kudlow, the director of the National Economic Council who had accompanied Trump to the summit of wealthy nations on Saturday, said on CNN's State of the Union.
Navarro told Fox News Sunday: "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."
Trudeau, in Quebec City for bilateral meetings with non-G7 leaders after the summit, did not respond to reporters' questions as he arrived, but his office pointed to Freeland as the minister responsible for Canada-US relations.
When Trump's tweets withdrawing support from the G7 statement hit on Saturday, the prime minister's office said Trudeau had not said anything in his closing news conference he has not said to Trump before.
Freeland told reporters that she had met with US Trade Representative Robert Lighthizer on Friday and would speak to him later on Sunday, adding that she believes a deal to renew the North American Free Trade Agreement is still possible.
"We are convinced that a modernisation is perfectly possible, we are convinced that common sense will triumph," she said.
Some 75 per cent of Canadian exports go to the US, making Canada uniquely vulnerable to a US trade war.