BRUSSELS (AP) — After three years spent trying to deter Russia from destroying Ukraine, European Union leaders grappled on Monday with how to respond to a major ally who appears determined to start a trade war or even seize part of their territory.

It would "be a cruel paradox if, during the time of this direct Russian threat and Chinese expansion," the EU and the United States might end up in a "conflict among allies," said Polish Prime Minister Donald Tusk, whose country currently holds the EU's rotating presidency.

Since taking office last month, U.S. President Donald Trump has threatened to impose tariffs on EU imports and refused to rule out military force to take control of Greenland, an autonomous territory of NATO ally Denmark.

Trump has also mystified Europeans by showing little sign of how he intends to end the war in Ukraine within six months as promised, let alone in a day, as he boasted while campaigning last year.

“We have to do everything to avoid this totally unnecessary and stupid tariff war or trade war,” the Polish prime minister told reporters in Brussels, where EU leaders met for talks on boosting and improving military spending and ramping up Europe’s defense industry.

Tusk said Trump’s threats amount to “a serious test” of European unity, and “in a very strange context, because it’s the first time where we have such a problem among allies.”

French President Emmanuel Macron said the EU is “a power that stands its ground” and that if hit with tariffs, the 27-nation bloc “would have to make itself respected.” He said Trump’s threats are “pushing Europeans to be more united, more active in addressing their collective security challenges.”

Trump slapped tariffs on European steel and aluminum during his first term, and EU leaders have already been in contact with Canadian Prime Minister Justin Trudeau since Canada imposed retaliatory duties on U.S. goods in response to a 25% tariff levied by Trump. The U.S. president later on Monday agreed to a 30-day pause on his tariff threat as America's two largest trading partners took steps to appease his concerns about border security and drug trafficking.

European Commission President Ursula von der Leyen underlined that ties between the bloc and the United States are part of “our most consequential relationship. It is fundamental to promoting peace, security and prosperity.”

But she warned that “there are clearly new challenges and growing uncertainty” and the EU stands ready to defend itself. “When targeted unfairly or arbitrarily, the European Union will respond firmly,” von der Leyen told reporters after the meeting.

Meanwhile, Denmark's prime minister again insisted on Monday that Greenland isn't for sale and called for a robust response from the EU should U.S. Trump press ahead with his threat to take control of the island.

“I will never support the idea of fighting allies. But of course, if the U.S. puts tough terms on Europe, we need a collective and robust response,” Danish Prime Minister Mette Frederiksen told reporters.

Last month, Trump left open the possibility that the American military might be used to secure Greenland, as well as the Panama Canal. "We need Greenland for national security purposes," he said.

Frederiksen said she has “great support” from her EU partners on the fact “that everybody has to respect the sovereignty of all national states in the world, and that Greenland is today a part of the Kingdom of Denmark. It’s part of our territory and it’s not for sale.”

European Council President Antonio Costa, noting that the EU has stood beside Ukraine in defense of its borders, said of Greenland: “Of course, we will stand also for these principles, all the more so if the territorial integrity of a member state of the European Union is questioned.”

Frederiksen acknowledged U.S. concerns about security in the Arctic Region, where Russia and China have been increasingly active.

“I totally agree with the Americans that the High North, that the Arctic region is becoming more and more important when we are talking about defense and security and deterrence,” Frederiksen said, adding that the U.S. and Denmark could have “stronger footprints” in Greenland, in security terms.

“They are already there and they can have more possibilities,” she said, underlining that Denmark itself can also “scale up” its security presence. “If this is about securing our part of the world, we can find a way forward,” Frederiksen said.

Last week, her government announced a roughly 14.6 billion kroner (nearly $2 billion) agreement with parties including the governments of Greenland and the Faeroe Islands to “improve capabilities for surveillance and maintaining sovereignty in the region.”

It would include three new Arctic naval vessels, two additional long-range surveillance drones and satellite capacity, the Danish Defense Ministry said.

European Commission President Ursula von der Leyen addresses a media conference at the end of an EU summit in Brussels, Monday, Feb. 3, 2025. (AP Photo/Omar Havana)

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Poland's Prime Minister Donald Tusk addresses a media conference at the end of an EU summit in Brussels, Monday, Feb. 3, 2025. (AP Photo/Omar Havana)

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European Commission President Ursula von der Leyen, left, European Council President Antonio Costa, center, and Poland's Prime Minister Donald Tusk arrive at the European Council building after an EU summit in Brussels, Monday, Feb. 3, 2025. (AP Photo/Omar Havana)

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Denmark's Prime Minister Mette Frederiksen, left, speaks with Poland's Prime Minister Donald Tusk as they arrive for an EU summit at the Egmont Palace in Brussels, Monday, Feb. 3, 2025. (AP Photo/Geert Vanden Wijngaert)

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NATO Secretary General Mark Rutte addresses minsters on the other side of the room during an EU summit at the Egmont Palace in Brussels, Monday, Feb. 3, 2025. (AP Photo/Geert Vanden Wijngaert, Pool)

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Denmark's Prime Minister Mette Frederiksen arrives for an EU summit at the Egmont Palace in Brussels, Monday, Feb. 3, 2025. (AP Photo/Geert Vanden Wijngaert)

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French President Emmanuel Macron, left, speaks with Slovenia's Prime Minister Robert Golob at a round table meeting during an EU summit in Brussels, Monday, Feb. 3, 2025. (AP Photo/Geert Vanden Wijngaert)

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Italy's Prime Minister Giorgia Meloni attends a round table meeting during an EU summit at the Egmont Palace in Brussels, Monday, Feb. 3, 2025. (AP Photo/Geert Vanden Wijngaert)

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Germany's Chancellor Olaf Scholz, second left, speaks with Czech Republic's Prime Minister Petr Fiala, left, at a round table meeting during an EU summit in Brussels, Monday, Feb. 3, 2025. (AP Photo/Geert Vanden Wijngaert)

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Hungary's Prime Minister Viktor Orban, left, speaks with Belgium's Prime Minister Bart De Wever at a round table meeting during an EU summit in Brussels, Monday, Feb. 3, 2025. (AP Photo/Geert Vanden Wijngaert)

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Germany's Chancellor Olaf Scholz holds a cup and saucer during an EU summit at the Egmont Palace in Brussels, Monday, Feb. 3, 2025. (AP Photo/Geert Vanden Wijngaert)

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Greece's Prime Minister Kyriakos Mitsotakis, right, arrives for an EU summit at the Egmont Palace in Brussels, Monday, Feb. 3, 2025. (AP Photo/Geert Vanden Wijngaert)

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Britain's Prime Minister Keir Stammer, left, is greeted by NATO Secretary General Mark Rutte prior to a meeting at NATO headquarters in Brussels, Monday, Feb. 3, 2025. (AP Photo/Omar Havana, Pool)

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