White House trade adviser Peter Navarro has apologized for saying Justin Trudeau earned “a special place in hell” with his response to Donald Trump’s complaints about US-Canada trade.

Speaking at a conference in Washington on Tuesday, Navarro said his “job” in appearing on Fox News Sunday in the chaotic aftermath of the G7 summit in Quebec had been “to send a signal of strength”.

“The problem was that in conveying that message I used language that was inappropriate,” he said. “I own that. That was my mistake, those were my words.”

On Sunday, Navarro told Fox host Chris Wallace he was communicating “the sentiment that was on Air Force One”.

Canada’s prime minister earned Trump’s ire by giving a press conference, after the US president left La Malbaie, in which he spoke critically of US trade policy and said Canada would “move forward with retaliatory measures” in response to Trump’s move to impose tariffs on aluminum and steel.

Trump was by then on his way to his summit with North Korean leader Kim Jong-un in Singapore, having left the G7 early and after a press conference of his own in which he complained about trade. He reacted to Trudeau’s remarks by withdrawing the US from a G7 communique and criticising the prime minister fiercely by tweet.

The next morning, Navarro and chief economics adviser Larry Kudlow were deployed to the Sunday talk shows.

In a display of calculated aggression, Kudlow thumped the table as he told CNN’s State of the Union Trudeau had “stabbed us in the back” and instigated “a betrayal”.

Navarro then appeared on Fox News Sunday.

“There’s a special place in hell,” he said, “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.”

Deploying distinctly Trumpian nicknames for the Canadian leader, Navarro said: “And that’s what Bad Faith Justin Trudeau did with that stunt press conference. That’s what Weak Dishonest Justin Trudeau did and that comes right from Air Force One.”

Responding, Wallace said: “You used some very strong words, ‘stab in the back’, ‘a special place in hell’. You said that that came from Air Force One. Are those the …words of the president towards Trudeau?”

Navarro said: “Those were my words but they’re the sentiment that was on Air Force One.”