Donald Trump’s trade adviser has labelled Canadian premier Justin Trudeau a back-stabber unworthy of the US president’s time after the acrimonious end to the G7 summit.

“There’s a special place in hell for any foreign 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,” Peter Navarro said.

Canada’s foreign minister Chrystia Freeland said her country “does not conduct its diplomacy through ad hominem attacks”.

The verbal volleys by Mr Navarro and Mr Trump’s top economic adviser, Larry Kudlow, picked up where Mr Trump left off on Saturday evening with a series of tweets from Air Force One en route to Singapore for his nuclear summit on Tuesday with North Korea’s Kim Jong Un.

Trump G-7
Donald Trump and Justin Trudeau have been at loggerheads over trade tariffs (Evan Vucci/AP)

Mr Kudlow suggested Mr Trump saw Mr Trudeau as trying to weaken his hand before that meeting, saying the president will not “let a Canadian prime minister push him around … Kim must not see American weakness.”

Just as the G7 meeting of the world’s leading industrialised nations had seemed to weather Mr Trump’s threats of a trade war, the president backed out of the group’s joint statement that Mr Trudeau said all the leaders had come together to sign.

He called Mr Trudeau “dishonest & weak” after Mr Trudeau said at a news conference that Canada would retaliate for new US tariffs.

Mr Trudeau did not respond to questions about Mr Trump when the prime minister arrived at a Quebec City hotel on Sunday for meetings with other world leaders, though Mr Freeland later told reporters that “we don’t think that’s a useful or productive way to do business”.

A Trudeau spokesman, Cameron Ahmad, said on Saturday night that Mr Trudeau “said nothing he hasn’t said before — both in public and in private conversations” with Mr Trump.

And Roland Paris, a former foreign policy adviser to Mr Trudeau, jabbed at Mr Trump on Twitter: “Big tough guy once he’s back on his airplane. Can’t do it in person. … He’s a pathetic little man-child.”

Mr Trudeau said he had reiterated to Mr Trump, who left the G7 meeting before it ended, that tariffs would harm industries and workers on both sides of the US-Canada border.

He told reporters that imposing retaliatory measures “is not something I relish doing” but that he wouldn’t hesitate to do so because “I will always protect Canadian workers and Canadian interests”.

Mr Navarro said Mr Trump “did the courtesy to Justin Trudeau to travel up to Quebec for that summit. He had other things, bigger things, on his plate in Singapore. … He did him a favour and he was even willing to sign that socialist communique. And what did Trudeau do as soon as the plane took off from Canadian airspace? Trudeau stuck our president in the back. That will not stand.”