The US general who is NATO's supreme commander in Europe said meanwhile that the military alliance was having "healthy" talks on Greenland's importance.

Swedish Prime Minister Ulf Kristersson condemned US "threatening rhetoric" after Trump repeated that Washington was "going to do something on Greenland, whether they like it or not".

"On the contrary, the United States should thank Denmark, which over the years has been a very loyal ally," Kristersson said at a conference on Swedish defence.

"Sweden, the Nordic countries, the Baltic states, and several major European countries stand together with our Danish friends," he said.

Kristersson stressed a US takeover of the mineral-rich Arctic territory would be "a violation of international law and risks encouraging other countries to act in exactly the same way".

"It is a dangerous path to take," he added.

- No 'immediate threat' -

Meanwhile, Germany reiterated its support for Denmark and Greenland ahead of meetings in Washington on Monday.

Before talks with US Secretary of State Marco Rubio, German Foreign Minister Johann Wadehpul will stop Sunday in Reykjavik to address the "strategic challenges of the Far North", according to the foreign ministry statement.

"The legitimate interests of all NATO Allies, as well as those of the inhabitants of the (Arctic) region, must be at the centre of our discussions," Wadehpul said in the statement.

"It is clear that it is exclusively up to Greenland and Denmark to decide questions of Greenland's territory and sovereignty," he previously told Germany's Bild daily.

"We are strengthening security in the Arctic together, as NATO allies, and not against one another," German Finance Minister Lars Klingbeil said ahead of a global summit on critical raw materials in Washington.

European capitals have scrambled to coordinate a response after the White House said this week that Trump wanted to buy Greenland and refused to rule out military action.

Trump says controlling the island is crucial for US national security given the rising military activity of Russia and China in the Arctic.

NATO Supreme Allied Commander General Alexus Grynkewich told the Swedish defence conference that alliance members were having talks on Greenland's future. The US general added that while there was "no immediate threat" to NATO territory, the Arctic's strategic importance is fast growing.

Grynkewich said he would not comment on "the political dimensions of recent rhetoric" but that the 32 member alliance was holding talks on Greenland within its North Atlantic Council.

"Those dialogues continue in Brussels. They have been healthy dialogues from what I've heard," the general said.

"Members of the alliance, who have worked together for so many years, are talking together and working through these thorny issues."

A Danish colony until 1953, Greenland gained home rule 26 years later and is contemplating eventually loosening its ties with Denmark.

The vast majority of its population and political parties have said they do not want to be under US control and insist Greenlanders must decide their future.

"I don't think there's an immediate threat to NATO territory right now," Grynkewich told the defence conference. But he said Russian and Chinese vessels had been seen patrolling together on Russia's northern coast and near Alaska and Canada, seeking to work together to get greater access to the Arctic as ice recedes from global warming.