COPENHAGEN (Reuters) -The United States is exerting "unacceptable pressure" on Greenland, Denmark's Prime Minister Mette Frederiksen said on Tuesday, ahead of an unsolicited visit by a high-profile U.S. delegation to the semi-autonomous Danish territory this week.

The visit, which runs from Thursday to Saturday, will be led by Usha Vance, wife of U.S. Vice President JD Vance, and include White House National Security Adviser Mike Waltz and Energy Secretary Chris Wright.

President Donald Trump on Monday reiterated his suggestion that the U.S. should take over Greenland, saying the vast island was important for U.S. national security. Frederiksen has rejected the proposal.

"I have to say that it is unacceptable pressure being placed on Greenland and Denmark in this situation. And it is pressure that we will resist," she told Danish broadcasters DR and TV2.

Greenland's acting head of government, Mute Egede, has labelled the visit a "provocation," as it coincides with government coalition talks and municipal elections scheduled for the following week.

Since Donald Trump Jr.'s private visit to the mineral-rich island in January, Trump has consistently discussed U.S. annexation of Greenland.

On Monday, Trump said that his administration was working with "people in Greenland" who want something to happen, but did not elaborate.

"The visit is clearly not about what Greenland needs or wants," said Frederiksen. "President Trump is serious. He wants Greenland. Therefore, (this visit) cannot be seen independently of anything else," said Frederiksen.

Brian Hughes, spokesman for the White House National Security Council, said the delegation aimed to "learn about Greenland, its culture, history, and people."

Frederiksen disputed the notion of a private visit with official representatives. She said Denmark did not oppose ties with the United States, citing a 1951 bilateral agreement which established U.S. rights to move freely and construct military bases in Greenland, given Denmark and Greenland are notified.

"We are allies," she said, adding: "There is no indication either in Denmark or Greenland that we do not want cooperation with the Americans."

Egede has called for more robust support from allies against the U.S.

"There is massive support from the Nordic countries and the EU, so we have our allies and close partners with us," said Frederiksen.

(Reporting by Jacob Gronholt-Pedersen and Louise Breusch Rasmussen, editing by Terje Solsvik and Philippa Fletcher)