Greenland, the self-ruling territory of Denmark, told the United States Friday, "We are open for business, not for sale."Greenland's foreign minister dismissed the idea of Denmark selling the territory.One day earlier, The Wall Street Journal reported that U.S. President Donald Trump had spoken with his advisers about possibly buying the world's biggest island.The newspaper reported that Trump repeatedly expressed interest in buying Greenland. He even asked the White House counsel to explore the idea.The report surfaced ahead of Trump's planned visit to Denmark in September.He is set to meet with the prime minsters of Denmark and Greenland. The Journal said that the planned visit is unrelated to the idea of buying Greenland.Some Danish politicians have laughed at the idea."It has to be an April Fool's joke," wrote former prime minister Lars Lokke Rasmussen. His comments appeared on Twitter.Another politician, Soren Espersen, told Danish broadcaster DR, "If he is truly contemplating this, then this is final proof, that he has gone mad."