Without elaborating on the plan, President Donald Trump asserted early on Wednesday that "massive oil, gas and mineral exploitation is getting ready to begin" in Greenland.

Just after midnight, he posted on Truth Social, "There are experts that are saying that the amount of easily available oil is far greater than that of almost any land, anywhere in the world."

Trump has frequently threatened to seize control of Greenland, an autonomous region of Denmark, or to get access to its natural resources, notably its abundant and unexplored minerals, since taking office again, infuriating close European and NATO allies.

Because many of Greenland's mineral riches are found in isolated locations above the Arctic Circle, where there is a mile-thick polar ice sheet, researchers have previously indicated that it would be exceedingly difficult and costly to harvest the island's minerals. The ice covers over 80% of the island.

In response to Trump's threats to annex the strategically important island, the US, Denmark, and Greenland came to an agreement last month that was meant to ease tensions.

Denmark's sovereignty and Greenlanders' right to self-determination are acknowledged at the outset of the pact, which Trump claimed at the time provided the US "permanent control" over Greenland's security.

According to a text of the agreement posted on the White House website, the agreement, which modifies a 1951 treaty that permits the US to station troops in Greenland as part of NATO's defense, acknowledges "minerals cooperation" and "cooperation on economic development and business promotion," but it makes no mention of oil or gas.

Additionally, it guaranties US military access in the event that Greenland separates from Denmark and opens the door for more US bases.

"Any future attack on the United States will have to come across Greenland, where our Defense will routinely knock down drones, missiles, or any other form of weapon not yet even conceived," Trump wrote in his post on Wednesday.

CNN has requested comments from the government and Mineral Resources Authority of Greenland, the Danish Prime Minister's Office, and the White House.