Denmark's Prime Minister Mette Frederiksen accused the United States of exerting "unacceptable pressure" on Greenland and her country as US Vice-President JD Vance announced he would join what was meant to be a cultural visit to the Danish Arctic territory this week by his wife, Usha Vance.

What began as a proposed goodwill tour has escalated into a diplomatic flashpoint amid the US administration's continued interest in acquiring the Danish territory.

US President Donald Trump, who has previously proposed purchasing Greenland, declared controlling it was "an absolute necessity" in his State of the Union address this month, stating: "We need Greenland for national security. One way or the other we're going to get it."

Tensions with Denmark and Greenland escalated after Vance cited "Arctic security issues" as the focus for his visit in an official statement on Tuesday, having earlier said in a video message he was joining his wife's trip due to "so much excitement" around the planned cultural exchange.

The visit, from Thursday to Sunday, will include a stop at the Pituffik space base, the northernmost US military installation. The trip itinerary was revised amid criticism and after the vice-president's decision to join, with National Security Adviser Mike Waltz removed from the delegation and the focus shifted to the military base, reported Euronews.

"We're going to check out how things are going there," Vance said in the video shared online. "Speaking for President Trump, we want to reinvigorate the security of the people of Greenland because we think it's important to protecting the security of the entire world."

The visit comes as Greenland is still negotiating to form a new coalition government following a March 11 general election.

Before Vance's announcement, Frederiksen told Danish channel TV 2: "This is clearly not a visit that is about what Greenland needs or wants. That's why I have to say that the pressure being put on Greenland and Denmark in this situation is unacceptable. And it's pressure we will resist."

The Danish leader dismissed any notion of this being a private visit, stating: "You can't organize a private visit with official representatives of another country."

Speaking with Danmarks Radio, Frederiksen said: "President Trump is serious ... He wants Greenland. Therefore, it cannot be seen independently of anything else."

Even before Vance's announcement that he would join his wife, tensions were mounting as Greenland's government posted on Monday that it had "not extended any invitations for any visits, neither private nor official".

Despite Greenland's assertion, Trump countered on Monday: "We've been invited."

Frederiksen added: "When you make a visit like this and the Greenlandic politicians say they don't want this visit, you can't interpret that as respectful."