Paris, France - France and Germany on Wednesday warned Donald Trump against threatening "sovereign borders" after the US president-elect refused to rule out military action to take Greenland.

"There is no question of the EU letting other nations in the world, whoever they may be... attack its sovereign borders," French Foreign Minister Jean-Noel Barrot told France Inter radio.

"We are a strong continent. We need to strengthen ourselves more," he added.

"If you ask me: 'Is the United States going to invade Greenland?' the answer is no," said Barrot.

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But he added: "We have entered an era that is seeing the return of the law of the strongest."

"Should we be intimidated? Should we be overcome with worry? Evidently, no. We need to wake up and reinforce ourselves, militarily, in competition, in a world where the law of the strongest prevails."

In Berlin, German government spokesperson Steffen Hebestreit said in response to Trump's remarks that "as always, the firm principle applies... that borders must not be moved by force."

Trump set off new alarm on Tuesday at a press conference when he refused to rule out military intervention over the Panama Canal and Greenland, both of which he has said he wants the United States to control.

"We need Greenland for national security purposes," he declared.

His comments coincided with a private visit by his son Donald Trump Jr.

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Barrot said he believed that the US is "inherently not imperialistic" and said he "did not believe" that it is changing.

However, French government spokesperson Sophie Primas told reporters after a cabinet meeting that there was a "form of imperialism" in Trump's comments.

"Today we are seeing the rise in blocs, we can see this as a form of imperialism, which materializes itself in the statements that we saw from Mr. Trump on the annexation of an entire territory."

"More than ever, we and our European partners need to be conscious, to get away from a form of naivety, to protect ourselves, to rearm," she added.