North American Aerospace Defence Command (Norad) aircraft will soon arrive at a U.S. military base in Greenland for “long-planned” activities, the organization said Monday. The announcement from Norad, a joint U.S.-Canada military organization for aerospace monitoring and defence, came amid rising tensions over U.S. President Donald Trump’s demand for U.S. control of the autonomous Danish territory. The statement did not describe the nature of the planned activities at Pituffik Space Base, which it said were aimed at “defence cooperation.” It said that the activities had been coordinated with Denmark and that Greenland had been informed. Norad said that the arriving aircraft will operate alongside those from bases in the continental United States and Canada. “They will support various long-planned Norad activities, building on the enduring defence cooperation between the United States and Canada, as well as the Kingdom of Denmark,” Norad said. The statement added that Norad “routinely conducts sustained, dispersed operations in the defence of North America.” Trump has stoked anxiety among U.S. transatlantic allies with threats to take over Greenland “one way or the other.” Over the weekend, the U.S. president threatened to wield new tariffs against countries which oppose his plans for the Arctic island, after several European nations sent small military delegations there for an exercise, to which the United States was also invited. Denmark has proposed that NATO start surveillance operations in Greenland to confront security concerns.