Under the army's rules of engagement, Danish soldiers would have to shoot first and ask questions later if the United States invades Greenland, The Telegraph writes.
On Wednesday, the Danish Ministry of Defense confirmed the existence of a 1952 rule that requires soldiers to counterattack "immediately" invading forces without waiting for orders.
The Ministry of Defense also said the rule "remains in force" when asked about its status by Berlingske, a center-right Danish newspaper, reports the Telegraph.
This week, Donald Trump, the US president, has reiterated his intention to annex the NATO territory of Greenland, which he considers essential to US national security, including by military force if necessary.
His remarks have shocked Denmark - which governs Greenland as a foreign territory and insists the island is "not for sale" - as well as the Greenland government and the wider NATO alliance.
According to the Danish newspaper Berlingske, the 1952 rule states that in the event of an invasion, "forces must immediately undertake war without waiting for or seeking orders, even if the commanders in question are unaware of the declaration of war or the state of war."
When asked for comment, the Danish Ministry of Defense told the newspaper: "The order on precautionary measures for military defense in the event of attacks on the country and during war remains in force."
European allies are holding urgent talks on how to respond to a possible US attack on Greenland, a move that experts say would probably spell the end of the NATO alliance.
"We want to take action, but we want to do this together with our European partners," said Jean-Noël Barrot, the French foreign minister, of discussions on how Europe should respond to a US invasion of the Arctic island.
A German government source told Reuters news agency separately that Germany is "working closely together with other European countries and Denmark on the next steps regarding Greenland."
Also on Wednesday, Barrot suggested that he had received assurances from Marco Rubio, the US Secretary of State, that Washington was not planning an "invasion".
"I myself was on the phone yesterday with US Secretary of State Marco Rubio who confirmed that this was not the approach being followed, he ruled out the possibility of an invasion of Greenland," the French Foreign Minister said.
Rubio also informed US politicians that the threats against Greenland do not signal an imminent invasion, and that the goal is to buy the island, sources told the Wall Street Journal.
The WSJ report and Rubio's assurances appear to contradict Caroline Leavitt, Trump's press secretary, who said Tuesday that military action was "always an option."
At the same time, the Washington Post reported on Wednesday that US officials were increasingly discussing an invasion of Greenland with their European counterparts as a "concrete" possibility.
A senior European diplomat told the newspaper that there had been a noticeable change in tone on the issue in recent days. /Telegraph
