Denmark’s foreign minister summoned the top U.S. diplomat for talks after national media reported Wednesday that at least three people linked to President Donald Trump have conducted covert influence operations in Greenland.

Trump has repeatedly said he seeks U.S. jurisdiction over Greenland, a vast, semi-autonomous territory of Denmark. He has not ruled out military force to take control of the mineral-rich, strategically located Arctic island.

Denmark, a NATO ally of the U.S. and Greenland have said the island is not for sale and condemned reports of the U.S. gathering intelligence there.

Danish public broadcaster DR reported Wednesday that government and security sources, which it didn’t name, as well as unidentified sources in Greenland and the U.S., believe that at least three Americans with connections to Trump have been carrying out covert influence operations in the territory.

One of those people allegedly compiled a list of U.S.-friendly Greenlanders, collected names of people opposed to Trump and got locals to point out cases that could be used to cast Denmark in a bad light in American media. Two others have tried to nurture contacts with politicians, businesspeople and locals, according to the report.