Greenland is not for sale, Danish Prime Minister Mette Fredriksen said on Monday, after U.S. Secretary of State Marco Rubio said last week that President Donald Trump's interest in acquiring the island was "not a joke".

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.

The Financial Times reports that Trump threatened Denmark's prime minister in a "horrendous" 45-minute phone call. From the reportage, you get the impression that Mette Frederiksen hadn't considered the possibility Trump was serious about Greenland and wasn't briefed on how to address the subject.