Denmark summoned the US ambassador on Monday after US President Donald Trump appointed a special envoy to Greenland who immediately vowed to make the Danish autonomous territory "a part of the US".
Since returning to the White House in January, Trump has repeatedly said the United States "needs" the resource-rich Arctic island for security reasons and has refused to rule out using force to secure it.
On Sunday, Trump appointed Louisiana governor Jeff Landry as special envoy to Greenland.
Danish Foreign Minister Lars Lokke Rasmussen said on Monday 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.
In a post on his social media platform Truth Social, Trump said Landry understood "how essential Greenland is to our national security, and will strongly advance our country's interests for the safety, security, and survival of our allies, and indeed, the world".
Landry responded directly to Trump in a post on X: "It's an honour to serve you in this volunteer position to make Greenland a part of the US."
The Danish foreign minister 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.
Greenland Prime Minister Jens-Frederik Nielsen and Danish Prime Minister Mette Frederiksen said in a joint statement: "You cannot annex another country.
"We expect respect for our joint territorial integrity."
In a Facebook post addressed to Greenlanders, Nielsen said the appointment of a US special envoy had not changed anything for Greenlanders.
"We will determine our future ourselves. Greenland is our country," he wrote, adding: "Greenland belongs to Greenlanders."
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".
"These principles are essential not only for the European Union but for nations around the world. We stand in full solidarity with Denmark and the people of Greenland," they wrote on X.
- 'Show respect' -
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.
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.
Lokke Rasmussen said the appointment 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.
The US 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 US 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.
