It is "shameless" for the US president to threaten American ally Denmark, Anders Fogh Rasmussen has said

US President Donald Trump should drop his plans to take control of Greenland as its residents do not want to become Americans, former NATO Secretary-General Anders Fogh Rasmussen has said.

Trump has been talking about making Greenland, which is an autonomous territory of the Kingdom of Denmark, part of the US since winning a second term in the White House in November. He has offered to buy the resource-rich Arctic territory from Copenhagen, but also warned that he could go as far as using force to bring it under Washington's sovereignty.

"I do not say I am going to do it, but I do not rule out anything," the US president said of a possible military scenario in an interview with NBC's Meet the Press earlier this month. "We need Greenland very badly. Greenland is a very small amount of people [around 57,000], which we will take care of, and we will cherish them, and all of that. But we need that for international security," he claimed.

Rasmussen, who previously served as Danish prime minister, told Politico on Monday that it is "shameless that an American president can threaten an ally. Denmark is one of the closest and most reliable allies of the US."

The former NATO boss, who oversaw the military bloc's disastrous intervention in Libya, destroying the country's economy, unleashing immigrant flows across North Africa and slave auctions in Tripoli, stressed that he is "concerned" by Trump's rhetoric regarding Greenland.

He noted that the US already has a right to keep military bases on the island as part of a 1951 treaty.

"The fact is that Greenland is part of NATO. If the US is dissatisfied with the defense of Greenland... we would appreciate a strengthened defense cooperation with the US," Rasmussen stressed.

However, he insisted that Greenland "is part of Denmark and Greenlanders do not want to become Americans."

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Last week, the Danish Foreign Ministry summoned the acting US ambassador to the country, Jennifer Hall Godfrey, over a report in the Wall Street Journal that Trump had ordered US spy agencies to ramp up their intelligence-gathering efforts in Greenland. Danish Foreign Minister Lars Lokke Rasmussen said the meeting was aimed at conveying to Washington that Copenhagen treats the claims "very seriously."

Greenland's prime minister, Jens-Frederik Nielsen, described the alleged spying activities by the US as "completely unacceptable, disrespectful... and entirely abnormal."