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.

An influence operation is an organized effort to shape how people in a society think in order to achieve certain political, military or other objectives.

DR said its story was based on information from a total of eight sources, who believe the goal is to weaken relations with Denmark from within Greenlandic society.

DR said it had been unable to clarify whether the Americans were working at their own initiative or on orders from someone else. It said it knows their names but chose not to publish them in order to protect its sources. The Associated Press could not independently confirm the report.

“We are aware that foreign actors continue to show an interest in Greenland and its position in the Kingdom of Denmark,” Danish Foreign Minister Lars Løkke Rasmussen said in a statement emailed by his ministry. “It is therefore not surprising if we experience outside attempts to influence the future of the Kingdom in the time ahead.”

“Any attempt to interfere in the internal affairs of the Kingdom will of course be unacceptable,” Løkke Rasmussen said. “In that light, I have asked the Ministry of Foreign Affairs to summon the U.S. chargé d’affaires for a meeting at the Ministry.”

Cooperation between the governments of Denmark and Greenland “is close and based on mutual trust,” he added.

The U.S. Embassy in Copenhagen directed queries on the issue to Washington.

The Danish Security and Intelligence Service responded to a request for comment by saying it believes that “particularly in the current situation, Greenland is a target for influence campaigns of various kinds” that could aim to create divisions in the relationship between Denmark and Greenland.

It said it “assesses that this could be done by exploiting existing or fabricated disagreements, for example in connection with well-known individual cases, or by promoting or amplifying certain viewpoints in Greenland regarding the Kingdom, the United States, or other countries with a particular interest in Greenland.”

The service, known by its Danish acronym PET, said that in recent years it has “continuously strengthened” its efforts and presence in Greenland in cooperation with authorities there, and will continue to do so.