By LORNE COOK, Associated Press

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

Polish Prime Minister Donald Tusk said that it would “be a cruel paradox, if during the time of this direct Russian threat and Chinese expansion ” that the EU and the United States might end up in a “conflict among allies.”

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

Trump has also mystified the 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 during the election campaign last year.

Tusk, whose country currently holds the EU’s rotating presidency, said that 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.”

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

French President Emmanuel Macron said that the EU is “a power that stands its ground” and that if hit with tariffs, the bloc “would have to make itself respected.” He said that 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.

“We were listening carefully to (Trump’s) words, and of course we are preparing also on our side,” EU foreign policy chief Kaja Kallas said. But, she underlined, “there are no winners in trade wars. If … the U.S. starts a trade war, then the one laughing on the side is China.”

Meanwhile, Denmark’s prime minister 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.