OSLO: Denmark's prime minister voiced outrage on Friday (May 9) after media reports that Washington would step up spying in the Danish autonomous territory of Greenland, which is coveted by United States President Donald Trump.

The Wall Street Journal reported this week that US intelligence agencies had been ordered to find out more about its independence movement and opinions on American exploitation of resources.

According to the newspaper, intelligence agencies had been asked to identify people in Greenland and Denmark who support US objectives.

"Of course, you cannot spy against an ally," Danish Prime Minister Mette Frederiksen told reporters on the sidelines of a meeting of the Joint Expeditionary Force (JEF) coalition in Oslo.

Frederiksen noted that Denmark's Foreign Minister Lars Lokke Rasmussen had already been in contact with the US and that the reports were "rumours".

On Thursday, the charge d'affaires at the US embassy in Denmark Jennifer Hall Godfrey was summoned to a meeting at the Danish foreign ministry.

"We cannot tolerate people spying on each other. This message was sent very clearly today," Lokke told Danish broadcaster DR on Thursday.

"Spying in Nuuk by the United States is completely unacceptable. It is disrespectful," Greenland's Prime Minister Jens-Frederik Nielsen said.

Tensions between the US and Denmark have soared after Trump repeatedly said he wanted to take control of the resource-rich Arctic island.

The US president has insisted Washington needs control of Greenland for security reasons, refusing to rule out the use of force to secure it.