President Donald Trump on Monday reiterated that the United States needed Greenland for "national security" after his appointment of a special envoy to the Danish Arctic island triggered a new spat with Copenhagen.

Since returning to the White House in January, Trump has repeatedly said the United States "needs" the resource-rich autonomous territory for security reasons and has refused to rule out using force to secure it.

Trump on Sunday appointed Louisiana governor Jeff Landry as special envoy to Greenland, prompting anger from Denmark, which summoned the US ambassador.

"We need Greenland for national security. Not for minerals," Trump told a news conference in Palm Beach, Florida, on Monday.

"If you take a look at Greenland, you look up and down the coast, you have Russian and Chinese ships all over the place," he said.

"We need it for national security. We have to have it," the president said, adding that Landry "wanted to lead the charge".

On his appointment, Landry immediately vowed to make the Danish territory "a part of the US".

Danish Prime Minister Mette Frederiksen and Greenland's Prime Minister Jens-Frederik Nielsen earlier Monday said in a joint statement that Greenland belongs to Greenlanders.

"You cannot annex another country," they said. "We expect respect for our joint territorial integrity."

Danish Foreign Minister Lars Lokke Rasmussen said he was "deeply angered" by the move and warned Washington to respect Denmark's sovereignty.

The European Union later offered its "full solidarity" to Denmark.

The Danish foreign minister earlier told TV2 television the appointment and statements were "totally unacceptable" and, several hours later, said the US ambassador had been called up to the ministry for an explanation.

"We summoned the American ambassador to the foreign ministry today for a meeting, together with the Greenlandic representative, where we very clearly drew a red line and also asked for an explanation," Lokke Rasmussen told public broadcaster DR in an interview.

Strategic location

European Commission president Ursula von der Leyen and European Council president Antonio Costa stressed on social media that territorial integrity and sovereignty were "fundamental principles of international law".

Leaders of both Denmark and Greenland have repeatedly insisted that the vast island is not for sale and that it will decide its own future.

Most of Greenland's 57,000 people want to become independent from Denmark but do not wish to become part of the United States, according to an opinion poll in January.

Lokke Rasmussen said Trump's appointment of a special envoy confirmed continued US interest in Greenland.

"However, we insist that everyone -– including the US –- must show respect for the territorial integrity of the Kingdom of Denmark," he said in a statement emailed to AFP.

Washington argues Greenland, located between North America and Europe, can give it an economic edge over its rivals in the Arctic region.

The island has untapped rare earth minerals and could be a vital player as the polar ice melts and new shipping routes emerge.

Greenland's location also puts it on the shortest route for missiles between Russia and the United States.

The United States has its Pituffik military base in Greenland and opened a consulate on the island in June 2020.

In August, Denmark summoned the US charge d'affaires after at least three US officials close to Trump were seen in Greenland's capital Nuuk trying to find out how people felt about deepening US ties.

Trump's determination to take over Greenland has stunned Denmark, a fellow member of NATO that has fought alongside the US in its wars in Afghanistan and Iraq.

In January, Copenhagen announced a $2.0-billion plan to boost its military presence in the Arctic region.