"This is in our national interest and it needs to be solved," Rubio said. Greenland's prime minister has repeatedly said the island is not for sale.

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.

Secretary of State Marco Rubio said on Thursday he had "zero doubt" that China has a contingency plan to shut down the Panama Canal in the event of a conflict with the U.S. and that Washington intends to address what it sees as a national security threat.