PALM BEACH, Fla. — President-elect Donald Trump on Tuesday said he would not rule out the use of military force to seize control of the Panama Canal and Greenland, as he declared U.S. control of both to be vital to American national security.

Speaking to reporters less than two weeks before he takes office on Jan. 20 and as a delegation of aides and advisers that includes Donald Trump Jr. is in Greenland, Trump left open the use of the American military to secure both territories. Trump’s intention marks a rejection of decades of U.S. policy that has prioritized self-determination over territorial expansion.

“I’m not going to commit to that,” Trump said, when asked if he would rule out the use of the military. “It might be that you’ll have to do something. The Panama Canal is vital to our country.” He added, “We need Greenland for national security purposes.”

Greenland, home to a large U.S. military base, is an autonomous territory of Denmark, a longtime U.S. ally and a founding member of NATO. Trump cast doubts on the legitimacy of Denmark’s claim to Greenland.

The Panama Canal has been solely controlled by the eponymous country for more than 25 years. The U.S. returned the Panama Canal Zone to the country in 1979 and ended its joint partnership in controlling the strategic waterway in 1999.

Addressing Trump’s comments in an interview with Danish broadcaster TV2, Prime Minister Mette Frederiksen called the United States Denmark’s “most important and closest ally,” and that she did not believe that the United States will use military or economic power to secure control over Greenland.

Earlier, Trump posted a video of his private plane landing in Nuuk, the Arctic territory’s capital, in a landscape of snow-capped peaks and fjords.

“Don Jr. and my Reps landing in Greenland,” Trump wrote. “The reception has been great. They, and the Free World, need safety, security, strength, and PEACE! This is a deal that must happen. MAGA. MAKE GREENLAND GREAT AGAIN!”

In a statement, Greenland’s government said Donald Trump Jr.’s visit was taking place “as a private individual” and not as an official visit, and Greenlandic representatives would not meet with him.

Trump, a Republican, has also floated having Canada join the United States as the 51st state. He said Tuesday that he would not use military force to invade the country.

Promising a “Golden age of America,” Trump also said he would move to try to rename the Gulf of Mexico as the “Gulf of America,” saying that has a “beautiful ring to it.”