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. 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. Greenland's relationship with Denmark is complex; despite having broad self-government since 1979, its foreign and defence policy is made in Copenhagen. Although most of its political parties favor independence, they disagree on the pace of this move. While Greenlanders have had the right to call a referendum since 2009, polls suggest that most do not wish to become part of the US.