If an agreement regarding “the Complete and Total purchase of Greenland” by the United States is not reached by June 1, the rate is set to escalate to 25 percent, the announcement stated.

“The United States of America is open to immediate negotiations with Denmark or any other nation that has risked much, despite everything we have done for them,” Trump declared on Truth Social.

This tariff warning could signify a significant rift between Trump and America’s longstanding NATO allies, potentially further straining an alliance established in 1949 that offers mutual security for both Europe and North America.

Trump has frequently leveraged trade sanctions as a means to influence both allies and adversaries, securing investment pledges from some countries while facing resistance from others, particularly China.

Trump is expected to attend the World Economic Forum in Davos, Switzerland, where he is likely to encounter European leaders whom he recently threatened with tariffs set to take effect in just over two weeks.

French President Emmanuel Macron pushed back against Trump in a social media post that seemed to equate the threat to Russian leader Vladimir Putin’s war in Ukraine.

“No intimidation or threats will influence us, whether in Ukraine, Greenland or anywhere else in the world when we are faced with such situations,” Macron said in a translated post on X.

“Tariff threats are unacceptable and have no place in this context. Europeans will respond in a united and coordinated manner.”

There are immediate questions about how the White House could try to implement the tariffs because the EU is a single economic zone in terms of trading, according to a European diplomat who was not authorized to comment publicly and spoke on the condition of anonymity.

It was unclear, too, how Trump could act under US law, though he could cite emergency economic powers that are currently subject to a US Supreme Court challenge.

Trump has long said he thinks the U.S. should own the strategically located and mineral-rich island, which has a population of about 57,000 and whose defence is provided by Denmark.

He intensified his calls a day after the military operation to oust Venezuela’s Nicolas Maduro earlier this month.

The president indicated the tariffs were retaliation for what appeared to be the deployment of symbolic levels of troops from the European countries to Greenland, which he has said was essential for the “Golden Dome” missile defence system for the US.

He also has argued that Russia and China might try to take over the island.

The US already has access to Greenland under a 1951 defence agreement. Since 1945, the American military presence in Greenland has decreased from thousands of soldiers over 17 bases and installations to 200 at the remote Pituffik Space Base in the northwest of the island, the Danish foreign minister has said. That base supports missile warning, missile defence and space surveillance operations for the US and NATO.

Resistance has steadily built in Europe to Trump’s ambitions even as several countries on the continent agreed to his 15 per cent tariffs last year in order to preserve an economic and security relationship with Washington.

‘Important for the whole world’

Before Trump’s announcement, hundreds of people in Greenland’s capital, Nuuk, braved near-freezing temperatures, rain and icy streets to march in a rally in support of their own self-governance.

Thousands of people also marched through Copenhagen, many of them carrying Greenland’s flag. Some held signs with slogans such as “Make America Smart Again” and “Hands Off”.

“This is important for the whole world,” Danish protester Elise Riechie told The Associated Press as she held Danish and Greenlandic flags. “There are many small countries. None of them are for sale.”

The rallies occurred hours after a bipartisan delegation of US lawmakers, while visiting Copenhagen, sought to reassure Denmark and Greenland of their support.

Danish Major General Søren Andersen, told the AP that Denmark does not expect the US military to attack Greenland, or any other NATO ally, and that European troops were recently deployed to Nuuk for Arctic defence training.

He said the goal is not to send a message to the Trump administration, even though the White House has not ruled out taking the territory by force.

“I will not go into the political part, but I will say that I would never expect a NATO country to attack another NATO country,” he said from aboard a Danish military vessel docked in Nuuk.

“For us, for me, it’s not about signalling, it is actually about training military units, working together with allies.”

The Danish military organised a planning meeting on Friday in Greenland with NATO allies, including the US, to discuss Arctic security on the alliance’s northern flank in the face of a potential Russian threat.

The Americans were also invited to participate in Operation Arctic Endurance in Greenland in the coming days, Andersen said.

In his two and a half years as a commander in Greenland, Andersen said that he hasn’t seen any Chinese or Russian combat vessels or warships, despite Trump saying that they were off the island’s coast.

But in the unlikely event of American troops using force on Danish soil, Andersen confirmed that Danish soldiers have an obligation to fight back.

‘Almost no better’ ally to US than Denmark

Trump has contended that China and Russia have their own designs on Greenland and its vast untapped reserves of critical minerals. He said recently that anything less than the Arctic island being in US hands would be “unacceptable”.

The president has seen tariffs as a tool to get what he wants without having to resort to military actions. At the White House on Friday, he recounted how he had threatened European allies with tariffs on pharmaceuticals and he teased the possibility of doing so again.

“I may do that for Greenland, too,” Trump said.

After Trump followed through, Representative Don Bacon, a Republican in Nebraska, said, “Congress must reclaim tariff authorities” so that they are not used solely at a president’s discretion.

European leaders have said it is only for Denmark and Greenland to decide on matters concerning the territory, and Denmark said this week that it was increasing its military presence in Greenland in cooperation with allies.

“There is almost no better ally to the United States than Denmark,” said Senator Chris Coons while visiting Copenhagen with other members of Congress.

“If we do things that cause Danes to question whether we can be counted on as a NATO ally, why would any other country seek to be our ally or believe in our representations?”