Denmark and Greenland insist that the mineral-rich island is not for sale, while President Trump has not ruled out taking it by military force even though Denmark is a NATO ally.

Denmark Prime Minister Mette Frederiksen said "you cannot spy against an ally" after reports that the U.S. was gathering intelligence on Greenland.

Denmark says it will summon the top U.S. diplomat in the country for an explanation following a Wall Street Journal report about the United States stepping up its intelligence gathering on Greenland,