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".

UK Prime Minister Keir Starmer has publicly backed Denmark's sovereignty over Greenland, according to his spokesperson Dave Pares. This is the first time Starmer's government has publicly supported Denmark in the ongoing diplomatic crisis with the US over the Arctic territory.

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.