Any U.S. attempt to seize Greenland by force would trigger “monumental consequences” for the Western alliance and the global order, Iceland’s former President Olafur Ragnar Grimsson said, as President Donald Trump sharpens rhetoric on controlling the Arctic territory.

Grimsson warned on CNBC’s “Access Middle East” that “the fallout would be on a scale that we have never seen in living memory.” Grimsson, the longest-serving president of Iceland from 1996 to 2016, currently serves as the Chairman of the Arctic Circle, the world’s largest annual gathering on Arctic issues.

Trump has framed Greenland — an autonomous region within the Kingdom of Denmark — as central to U.S. national security, saying China and Russia were building up their presence in the region.

A meeting at the White House between officials from Greenland, Denmark and the U.S. Wednesday ended with “fundamental disagreement” over the ownership of the island, a Danish official said following the meeting, adding that both sides would continue to talk.

Trump doubled down on his rhetoric on Greenland ahead of the talks, saying on social media that anything less than Greenland becoming a part of the United States was “unacceptable.”