The US envoy to Denmark was summoned by the Danish foreign ministry on Wednesday, after the country’s public broadcaster reported that a number of American men have attempted to conduct “influence operations” in Greenland.

According to an investigation by Danish public broadcaster DR, at least three Americans with “ties” to US President Donald Trump are conducting active operations in Greenland, sparking concerns that they could be working to shift public opinion and push Trump’s desire to make Greenland a part of the US.

Greenland, a huge, resource-rich island in the Atlantic, is a self-governing territory of Denmark. Trump has repeatedly stated that he wants to annex the island, claiming that this is needed for security purposes. Both Greenland and Denmark are staunchly opposed to the idea.

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

According to the DR investigation, which was based off conversations with eight sources across Denmark, Greenland and the US, the three men are conducting the operations in an attempt to “infiltrate Greenlandic society.”

One of the American men involved has made a list of Trump supporters in Greenland, with the goal of later recruiting them to establish a secessionist movement on the island, according to the broadcaster.

The two other men have made contact with politicians, business people and other citizens, causing authorities to be concerned that they could be used to support Trump’s goal of annexing the territory, DR reported.

The broadcaster was unable to determine whether or not the men were acting under orders. CNN has reached out to the White House and the government of Greenland for comment.

“Any attempt to interfere” in Denmark’s internal affairs is “unacceptable,” Rasmussen said in Wednesday’s statement.

“The cooperation between the governments of Denmark and Greenland is close and based on mutual trust, just as there is close cooperation and dialogue between the relevant Greenlandic and Danish authorities,” he continued.