President Donald Trump said he may put a tariff on countries that "don't go along with Greenland" as he reiterated his demand for US control of the Danish territory.

Speaking during an event on Friday about rural health care in the US, President Donald Trump veered from talking about how he had once threatened European allies with tariffs on pharmaceuticals to doing the same thing to force countries in line with his designs on Greenland.

"I may do that for Greenland too," Trump said as an interjection. "I may put a tariff on countries if they don't go along with Greenland, because we need Greenland for national security. So I may do that," he said.

For months, Trump repeatedly said that the US should control the self-governing island that is part of the kingdom of Denmark.

However, this is the first time he or any of his administration have suggested using tariffs to force the issue.