Prime Minister Mette Frederiksen said that if Donald Trump were to attack the Danish island of Greenland that would mean the end of the NATO alliance.

“I believe one should take the American president seriously when he says that he wants Greenland,” Frederiksen said in an interview with Danish broadcaster TV2. “But I will also make it clear that if the U.S. chooses to attack another NATO country militarily, then everything stops, including NATO and thus the security that has been established since the end of the Second World War.”

Officials in Copenhagen have been alarmed by the U.S. president’s insistence on taking control of Greenland for security reasons following the raid on Caracas this weekend during which U.S. forces arrested Venezuelan President Nicolas Maduro.