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".
Merkel's statement came after Trump refused to endorse the final communique of the G7 summit and imposed tariffs on steel and aluminum imported from Europe, Canada and Mexico, sparking fears of a possible trade war.
Trump, who is in Asia for meetings with North Korean leader Kim Jong Un, tweeted that "Fair Trade is now to be called Fool Trade if it is not Reciprocal" and suggested that Canada is "bragging" in an unspecified release about benefiting from USA trade.
After comments Sunday by Kudlow and White House trade adviser Peter Navarro, Canada's foreign affairs minister said Ottawa "does not conduct its diplomacy through ad hominum attacks" and was justified in responding to Trump's tariffs.
Trudeau's office cast doubt over the genuineness of Trump's offense at the prime minister's remarks, pointing out that Trudeau's messages simply reiterated his position before the summit, that he will oppose attempts to bully Canada on trade.
"The historic and important agreement we all reached at #G7Charlevoix will help make our economies stronger & people more prosperous, protect our democracies, safeguard our environment and protect women & girls' rights around the world", Trudeau tweeted.More news: Kia Recalling 500K Vehicles
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Trump took more swipes at Canada and its prime minister over trade issues as he settled in for a summit with North Korea in Singapore, contending that "fair trade is now to be called fool trade if it is not reciprocal".
France has warned that "fits of anger" can not not dictate global cooperation after US President Donald Trump abruptly rejected a previously agreed joint statement in the wake of a fractious Group of Seven (G7) summit in Canada.
Trump is set to meet with the North's leader, Kim Jong Un, on Tuesday in Singapore in the first-ever summit between sitting leaders of the US and North Korea.
US President Donald Trump continued his ongoing verbal attacks on Canadian Prime Minister Justin Trudeau early on Monday saying that "Justin acts hurt when called out!" "We make our commitments and keep them".
"International cooperation can not depend on being angry and on sound bites. We will act too", she said. "We strive to reduce tariff barriers, non-tariff barriers and subsidies", it said.
Trump advisers described Trudeau's statements as a slight that threatened to make the USA look weak right as the president was leaving for a summit with North Korean dictator Kim Jong Un.
Abe stressed the unity of members in support of fair trade, while refraining from directly repeating Japan's concern about the US levies, during the two-day summit through Saturday in the Charlevoix region of Quebec.