Denmark, Norway, Sweden, France, Germany, the United Kingdom, the Netherlands and Finland are casting a united front after Trump threatens tariffs.

Denmark’s foreign minister said on Wednesday that a “fundamental disagreement” with U.S. President Donald Trump over the future of Greenland remained unresolved after high-level talks in Washington, even as Denmark and NATO allies moved to increase their military presence in the Arctic territory amid rising tensions.

Denmark and Greenland are stepping up their military presence on the island and allied reinforcements are expected to follow with Sweden confirming a deployment of military officers to the Arctic at Denmark’s request, according to a statement by prime minister Ulf Kristersson.

Prime Minister Mark Carney is considering sending soldiers to Greenland for military exercises with NATO allies, as U.S. President Donald Trump threatens tariffs on European nations unless they let him purchase and control the semiautonomous island,

TIME spoke to legal experts about whether Trump could legally pull the U.S. out of NATO and the wider implications.

Soldiers from European NATO countries are bracing for exceptionally challenging conditions during a reconnaissance mission aimed at strengthening security around Greenland. Denmark's top Arctic commander,

Denmark's Joint Arctic Command in Greenland is focused on countering potential Russian activity, not defending against U.S. military threats, its head Major General Soren Andersen said on Friday, amid renewed attention on the Arctic region.

Russia's ambassador to Denmark has accused NATO of seeking to militarize the Arctic amid US President Donald Trump's persistent threats to seize Greenland.