Denmark's foreign minister has summoned the top US diplomat in Copenhagen, following a report that American citizens have been conducting covert operations in Greenland.
Denmark's public broadcaster DR quoted sources as saying the aim was to infiltrate Greenland's society and promote its secession from Denmark to the US, although it was unable to clarify who the men were working for.
Danish intelligence warned Greenland was being targeted by 'various kinds of influence campaigns'.
Foreign Minister Lars Lokke Rasmussen said 'any attempt to interfere in the internal affairs of the Kingdom [of Denmark] will of course be unacceptable', and the US charge d'affaires had been summoned in that light.
The BBC has approached the US embassy and the state department for comment.
However, US President Trump has said several times he wants to annex Greenland, a semi-autonomous part of the Kingdom of Denmark, and Vice-President JD Vance has accused Copenhagen of underinvesting in the territory.
On a visit to Greenland a few months ago, Danish Prime Minister Mette Frederiksen warned the US that 'you cannot annex another country'.
Denmark's foreign minister said in a statement to the BBC that the government was '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,' he added.
Denmark is a member of Nato and the European Union and has long seen the US as one of its closest allies, and Danes have been shocked by Trump's determination to control its semi-autonomous territory. The US president said this year he would not rule out seizing it by force.
Denmark's PET security and intelligence service stated that influence campaigns would aim to 'create discord in the relationship between Denmark and Greenland'. This could be done by exploiting 'existing or invented disagreements' either with 'traditional, physical influence agents or via disinformation'. PET said it had strengthened its presence in Greenland and cooperation with local authorities.
The US currently has no ambassador in Copenhagen, so Rasmussen has summoned Mark Stroh, who as charge d'affaires is the most senior diplomat in the Danish capital.
Lars Lokke Rasmussen has already summoned the US charge d'affaires in Denmark this year in response to a separate report in May suggesting US spy agencies had been told to focus their efforts on Greenland.
DR's report detailed a visit by one American to Greenland's capital Nuuk, where he was seeking to compile a list of Greenlanders who backed US attempts to take over the island for recruitment in a secession movement.
The earlier May report in the Wall Street Journal also referred to learning more about Greenland's independence movement and attitudes toward American mineral extraction.
US Director of National Intelligence Tulsi Gabbard did not deny the report, accusing the Journal of 'breaking the law and undermining our nation's security and democracy'.
Greenland has a complex relationship with Denmark; despite being self-governing since 1979, its foreign and defense policy is directed by Copenhagen. Polls suggest the vast majority of Greenlanders do not wish to become part of the US.
Denmark's foreign minister's recent decision to summon the US charge amounts to a 'diplomatic yellow card', an unprecedented action in Danish-US relations, according to Jens Ladefoged Mortensen of the University of Copenhagen. 'This hostile attitude towards Denmark from the Trump administration is shocking,' he said.
In recent days, a major Danish company has faced US government scrutiny over a halted wind farm project off Rhode Island, further complicating bilateral relations.
