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.

Secretary of State Marco Rubio says President Donald Trump’s desire to acquire Greenland and retake control of the Panama Canal is driven by legitimate national security interests stemming from growing concerns about Chinese activity and influence in the Arctic and in Latin America.

The top US diplomat said President Donald Trump’s proposal to buy Greenland “is not a joke” because of the risk that China would station resources on the island that threaten American security and the importance of Arctic shipping lanes for energy exports.