Washington: President Donald Trump said Saturday he was sending a hospital boat to Greenland, an autonomous Danish territory that he has long coveted and threatened to seize by force.

Trump's rhetoric has ratcheted up tensions between the United States and Denmark, while putting the global spotlight on the Arctic as he insists mineral-rich Greenland is vital for US and NATO security against Russia and China.

He said the boat would treat many "sick" people in Greenland, without providing any details on who he was referring to or the number of people the vessel would help.

"We are going to send a great hospital boat to Greenland to take care of the many people who are sick, and not being taken care of there," Trump wrote in a social media post.

"It's on the way!!!," he added.

The post on his Truth Social platform carried an apparent AI image that depicted the USNS Mercy – an 894-foot (272-meter) vessel that is typically stationed in southern California – sailing toward snowcapped mountains on the horizon.

It was unclear if that was the actual vessel being sent to Greenland.

Trump said in the post that the ship would be sent in coordination with Gov. Jeff Landry (R-LA), who was named as Trump's envoy to the Arctic island in December.

During Mardi Gras celebrations in New Orleans this month, Landry posted an image of himself and two men at one of the city's famous balls, holding a flag of Greenland together.

"Great to host some of the wonderful people of Greenland," he wrote.

Earlier this week Denmark's King Frederik X visited Greenland, where he has long enjoyed popularity, as anxieties mount over Trump's interest.

Trump backed off repeated threats to seize the territory last month, after striking a "framework" deal with NATO chief Mark Rutte to ensure greater US influence. (AFP)