President Donald Trump's interest in buying Greenland is "not a joke," Secretary of State Marco Rubio said in an interview on Thursday, adding that acquiring Greenland was in U.S. national interest and needs to be solved.

Rubio said he could not predict if Trump would succeed in buying Greenland from Denmark or restoring American authority over the Panama Canal while he is in office.

President Trump told Denmark’s leader he wanted to take over Greenland, European officials say. Denmark has asked its E.U. allies not to inflame the situation until Mr. Trump’s intentions are clearer.