President Donald Trump says Canadian Prime Minister Justin Trudeau “learned” from the mistake of criticising him and it’s going to cost Canada “a lot of money".

At a news conference on Tuesday after his summit with North Korean leader Kim Jong Un, Trump recounted his recent tough exchanges with Trudeau. He said the Canadian leader must not have realised that Trump had televisions on Air Force One, allowing him to monitor Trudeau’s news conference at the end of the G-7 summit.

Trudeau had told reporters that Trump’s decision to invoke national security to justify US tariffs on steel and aluminum imports was “kind of insulting” to Canadian veterans who had stood by their US allies in conflicts dating back to World War I.

“Canadians are polite and reasonable but we will also not be pushed around,” he had said.

Trudeau said he had told Trump “it would be with regret but it would be with absolute clarity and firmness that we move forward with retaliatory measures on July 1, applying equivalent tariffs to the ones that the Americans have unjustly applied to us.”

At Tuesday's press conference, the president also discussed the viral photo taken of German Chancellor Angela Merkel and others standing before him. Trump said it was snapped as they waited for changes he’d requested to the communique that he ended up pulling out of.

Trump said it “didn’t look friendly” but it was “very friendly”.