North Korean leader Kim Jong Un "must not see American weakness" before his meeting Tuesday in Singapore with Trump, economic advisor Larry Kudlow said on CNN's "State of the Union."

Trump arrived in Singapore on Sunday for the summit, with Pyongyang's nuclear arsenal at the top of the agenda.

The US president has called it a "one-time shot" at peace.

Before leaving Canada for the summit the previous day, the US president took to Twitter to describe G7 host Trudeau as "very dishonest & weak."

Trump said he had instructed US representatives not to endorse the joint communique issued at the end of the summit.

The US president seemed particularly incensed by Trudeau's comments in a news conference criticizing Trump's decision to invoke national security to justify US tariffs on steel and aluminum imports.

That decision was "kind of insulting" to Canadian veterans who had stood by their US allies in conflicts dating back to World War I, Trudeau said.

"Canadians are polite and reasonable, but we will also not be pushed around," the prime minister said.