Danish Foreign Minister Lars Lokke Rasmussen on Wednesday said he had summoned the senior US diplomat in Copenhagen after reports that US citizens linked to US President Donald Trump's administration carried out influence operations in Greenland.

Reports of covert activity on the vast Arctic island, rich in minerals, threaten to strain ties between the two NATO allies.

Officials in Copenhagen view such foreign interference as an attack on national sovereignty. Rasmussen said Denmark "will of course" not accept covert operations on its territory.

What triggered Denmark's protest?

Public broadcaster DR reported that at least three US citizens with connections to the Trump administration had been involved in secret influence operations in Greenland. The individuals were not named.

Rasmussen said any interference in Danish internal affairs was "unacceptable" and ordered the Foreign Ministry to summon the US charge d'affaires.

DR said the three were trying to weaken ties between Denmark and Greenland, citing information from eight sources.

The broadcaster said it was unclear whether they were acting independently or under orders.

"We are aware that foreign actors continue to show an interest in Greenland and its position in the Kingdom of Denmark," the Danish Foreign Ministry said.

One of the three men reportedly worked on lists of Greenlanders who are respectively positive and negative toward the idea of ​​Greenland being under US control.

The US mission in Copenhagen is currently led by Mark Stroh. 

Why is Greenland important to the US?

Earlier revelations in the Wall Street Journal had reportedly reinforced the authorities' concerns about a US threat to Greenlandic democracy.

The newspaper said US Director of National Intelligence Tulsi Gabbard had directed intelligence agency heads to learn more about Greenland's independence movement and sentiment about US resource extraction there.

Trump has repeatedly said he wants the US to take over Greenland, citing its mineral wealth and strategic location in the Arctic. He has not ruled out using force, describing the island as vital for both national and international security.

Denmark has full sovereignty over Greenland, though the island has wide autonomy.

Edited by: Dmytro Hubenko