Danish authorities reportedly planned to sabotage key airstrips in Greenland to block any attempt by the United States to seize the island, according to a report by Denmark's public broadcaster DR.
DR says its account is drawn from a dozen senior sources in the Danish government and military, with two European officials later confirming elements of the story to the Financial Times.
The Danish defence ministry declined to comment to the BBC.
The move was allegedly part of a wider, discreet deployment to Greenland that included Danish troops and contingents from France, Germany, Norway and Sweden.
Forces were sent to Nuuk and the air hub at Kangerlussuaq, and supplies such as blood for treating casualties were reportedly brought in.
Officials framed the deployments as joint NATO exercises under the name Operation Arctic Endurance, but DR reports the real purpose was to prepare for the possibility of a US attempt to take control of the territory.
Sources say elite Danish soldiers and French cold-warfare units were among those sent north, alongside Danish aircraft and a French naval vessel.
Tensions stem from repeated public comments by then-US President Donald Trump about acquiring Greenland, which is a self-governing territory within the Kingdom of Denmark.
Copenhagen and Nuuk consistently rejected those proposals, and Danish sources told DR they took any talk of a US takeover seriously.
According to the broadcaster, concern intensified after reports of a US operation in Venezuela in early January that Danish officials saw as evidence Washington might act more boldly overseas.
A Danish defence source told DR planners wanted to ensure any attempt to seize the island would come at a cost, even if Danish forces could not repel a full-scale US attack.
French President Emmanuel Macron is reported to have backed the reinforcements, and European partners were asked to show solidarity through increased joint activity in Greenland.
DR quotes sources in France and Germany saying their governments were involved in political and military planning.
After the episode became public, Trump said he did not want to use force over Greenland and sought negotiations to resolve the dispute.
The episode highlights frictions between NATO allies over strategic Arctic territory and the sensitivities around sovereignty for Greenlanders and Danish authorities.
