Jon Rahbek-Clemmensen of Denmark's Syddansk University said the government in Copenhagen had staked its claim, partly to show the world that Denmark could not be pushed about, but also to prove a political point to the people of Greenland.

"There's a strong push for independence in Greenland, and Denmark wants to show it's capable of taking its interest into account," he told the BBC.

"By taking this step, Copenhagen is sending a signal [to Greenland]: 'Listen, we're on your team'."

A Russia submarine planted a rust-proof titanium flag 4,200m (14,000ft) beneath the North Pole in 2007, provoking an angry response from Canada.

Don't see how that works. Boundaries are based on coast line not on the continental shelf.