Prime Minister Justin Trudeau said Sunday he would speak with King Charles III about defending Canada's sovereignty, as President Donald Trump repeatedly calls for it to become the 51st US state.

Trump's comments have been met with outrage in Canada, with officials firmly rejecting any discussion of it ever becoming a part of the United States.

When he meets Monday with King Charles, who is Canada's head of state, Trudeau said he hopes to "discuss matters of importance to Canada and to Canadians."

"And I can tell you that nothing is more important to Canadians right now than standing up for our sovereignty and our independence as a nation," said the prime minister, while in London for a summit on Ukraine.

Trump has been particularly transfixed on Canadian sovereignty since winning a new term in November.

He regularly refers to Canada as the "51st state," and has demeaned Trudeau by calling him "governor," instead of prime minister.

Trump has ordered tariffs against the major US trading partner, set to go into effect Tuesday, while saying they could be avoided if Canada were part of the United States.

Trudeau last month warned that Trump's persistent talk about absorbing Canada to access its natural resources was "a real thing."

Some Canadians have wondered aloud why King Charles has not spoken out in defense of Canada.

It is custom that the monarch acts only on the advice of the prime minister in matters involving the Commonwealth nation.

Last week, British Prime Minister Keir Starmer invited Trump for an unprecedented second state visit to the UK, which could provide an opportunity for the king to raise the issue of Canadian sovereignty.

At the London summit on Ukrainian security on Sunday, Trudeau also reiterated Canada's strong and unwavering support for Ukraine, and announced new sanctions against Russia.