Donald Trump threatened military action to secure the Panama Canal and economic force against neighboring Canada in meandering remarks Tuesday that drew firm and frosty responses from the two US allies.

Speaking after Congress certified his election victory, the Republican president-elect gathered reporters at his home in southern Florida to announce a $20 billion Emirati investment in US technology. But his remarks quickly became a rally-style rant as he returned at length to familiar campaign themes.

"Since we won the election, the whole perception of the whole world is different. People from other countries have called me. They said, 'Thank you, thank you,'" Trump said as he set out his agenda for the coming four years.

The billionaire announced he was going to rename the Gulf of Mexico the "Gulf of America" and threatened the US's southern neighbor again with massive tariffs if it does not halt illegal border crossings.

He refused to rule out using military force to seize Greenland and the Panama Canal - both of which he has long coveted - criticising recently deceased Jimmy Carter for permitting a handover to local control of the Central American waterway when he was president.

Asked if he would use military force to bring Canada to heel, the incoming president said "no - economic force," but added that eliminating the "artificially drawn" US-Canada border would be a boon to national security.

As with many of Trump's pronouncements, it was difficult to separate humor or bombast from genuine policy, but the remarks will be seen as an escalation of his rhetoric on territorial expansion, and drew a dismissive response from across the border.

There is a "snowball's chance in hell" that Canada will merge with the United States, Prime Minister Justin Trudeau responded.

Panama's Foreign Minister Javier Martinez-Acha meanwhile said "the sovereignty of our canal is not negotiable."

Addressing a claim by Trump that Chinese soldiers operate the waterway connecting the Atlantic and Pacific, the minister said: "the only hands operating the canal are Panamanian and that is how it is going to stay."

A world that's burning

Built by the United States, the Panama Canal was handed to the Central American country a quarter-century ago and President Jose Raul Mulino has refused to entertain negotiations over its control.

"Look, the Panama Canal is vital to our country. It's being operated by China - China! - and we gave the Panama Canal to Panama, we didn't give it to China," Trump said. "And they've abused it, they've abused that gift."

Trump has also ruffled European feathers with a separate territorial proposal - to buy Greenland, an island abutting the emerging Arctic geopolitical battleground that the former real estate developer sees as important to US security.

Trump's eldest son, Donald Trump Jr., arrived on the island shortly before his father's remarks for what was described as a personal visit, with no official meetings scheduled.

Denmark - which Greenland is an autonomous territory of - is a US ally and a fellow member of NATO, another target of Trump's ire as he demanded that nations in the western alliance boost their defence spending.

"Europe is in for a tiny fraction of the money that we're in," Trump said. "We have a thing called the ocean in between us, right? Why are we in for billions and billions of dollars more money than Europe?"

Danish Prime Minister Mette Frederiksen told broadcaster TV2 she didn't "have the fantasy" Trump's plans for Greenland would ever get off the ground.

In his foreign-policy focused speech, Trump also hammered President Joe Biden over the US withdrawal from Afghanistan and the conflicts in Ukraine and Syria, repeating a favorite false claim that America "had no wars" during the first Trump term.

The president-elect - who spent much of the news conference focused on Biden - also hammered the White House over the 2025 transition, claiming that officials were "trying everything they can to make it more difficult."

Trump, who returns to the White House on January 20, has not acknowledged his 2020 defeat and refused to participate in the transfer of power to Biden.

He baselessly accused his rival of being behind the multiple legal challenges he faces and vowed to overturn the Democrat's executive order banning offshore oil and gas development off swathes of US coastline.

Later that evening, he posted internet memes showing Canada as part of the United States.

AFP

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Freewheeling Donald Trump sets out US territorial ambitions