President Trump reportedly held a “fiery” call with Denmark’s Prime Minister Mette Frederiksen over the president’s insistence that U.S. control of Greenland is necessary for American national security.

Greenland is a self-ruling territory in the Danish kingdom, which means policymakers in Nuuk control most domestic issues. Denmark, which oversees defense and security policy on the mineral-rich Arctic island, is injecting 14.6 billion kroner ($2 billion) to ramp up defenses.

Denmark is ready to allow the US to boost its presence in Greenland, Danish Prime Minister Mette Frederiksen said as she seeks to curb an escalating diplomatic crisis with the Trump administration over the world’s largest island.