President Donald Trump said Sunday the United States would take Greenland "one way or the other," warning that Russia and China would "take over" if Washington didn't act.

Trump says controlling the mineral-rich Danish territory is crucial for US national security given increased Russian and Chinese military activity in the Arctic.

"If we don't take Greenland, Russia or China will, and I'm not letting that happen," Trump told reporters aboard Air Force One, despite neither country laying claim to the vast island.

Trump said he would be open to making a deal with the Danish self-governing territory "but one way or the other, we're going to have Greenland."