By Jacob Gronholt-Pedersen

COPENHAGEN (Reuters) - Greenland on Friday dismissed the notion that it might be up for sale after reports that U.S. President Donald Trump had privately discussed with his advisers the idea of buying the world's biggest island.

"We are open for business, but we're not for sale," Greenland's foreign minister Ane Lone Bagger told Reuters.

Trump is due to visit Copenhagen in September and the Arctic will be on the agenda during meetings with the prime ministers of Denmark and Greenland, an autonomous Danish territory.

Talk of a Greenland purchase was first reported by the Wall Street Journal. Two sources familiar with the situation told Reuters that the notion had been laughed off by some advisers as a joke but was taken more seriously by others in the White House.

Danish politicians on Friday poured scorn on the idea.

"It has to be an April Fool's joke. Totally out of season," former prime minister Lars Lokke Rasmussen said on Twitter.

"If he is truly contemplating this, then this is final proof, that he has gone mad," foreign affairs spokesman for the Danish People's Party, Soren Espersen, told broadcaster DR.

"The thought of Denmark selling 50,000 citizens to the United States is completely ridiculous," he said.

Greenland, a self-ruling part of Denmark located between the North Atlantic and Arctic oceans, is dependant on Danish economic support. It handles its own domestic affairs while Copenhagen looks after defense and foreign policy.

"I am sure a majority in Greenland believes it is better to have a relation to Denmark than the United States, in the long term," Aaja Chemnitz Larsen, Danish MP from Greenland's second-largest party Inuit Ataqatigiit (IA), told Reuters.

"My immediate thought is 'No, thank you'," she said.

Prime Minister Mette Frederiksen and Foreign Minister Jeppe Kofod were not available for comment but officials said they would respond later on Friday. The U.S. Embassy in Copenhagen was also not immediately available for comment.

"Oh dear lord. As someone who loves Greenland, has been there nine times to every corner and loves the people, this is a complete and total catastrophe," former U.S. ambassador to Denmark, Rufus Gifford, said in on Twitter.

Greenland is gaining attention from global super powers including China, Russia and the United States due to its strategic location and its mineral resources.

In May, U.S. Secretary of State Mike Pompeo said Russia was behaving aggressively in the Arctic and China's actions there had to be watched closely as well.

A defense treaty between Denmark and the United States dating back to 1951 gives the U.S. military rights over the Thule Air Base in northern Greenland.

There has been no indication that a Greenland purchase will be on the agenda for Trump's talks with Danish officials.

Martin Lidegaard, senior lawmaker of the Danish Social Liberal Party and a former foreign minister, called the idea "a grotesque proposal" which had no basis in reality.

"We are talking about real people and you can't just sell Greenland like an old colonial power," he told Reuters.

"But what we can take seriously is that the U.S. stakes and interest in the Arctic is significantly on the rise and they want a much bigger influence," he added.

In 1917 Denmark sold off the then Danish West Indies islands for $25 million to the United States, which renamed them the United States Virgin Islands.

(Reporting by Nikolaj Skydsgaard, Andreas Mortensen, Stine Jacobsen and Jacob Gronholt-Pedersen; additional reporting by Steve Holland in the United States, Editing by Angus MacSwan)