France’s top diplomat fires a warning shot across the bows of Donald Trump, warning Europe considers Greenland part of its “sovereign borders” and should be left alone.

European leaders are reacting with alarm as past and future President Donald Trump talks up the importance of the United States acquiring Greenland, the world’s largest island and a strategically valuable if underdeveloped Arctic territory in the North Atlantic. As Trump’s son flew into Greenland on the Trump jet this week the French foreign minister has appeared to tacitly put the notion of the United States buying territory off an ally on a par, ethically, with the Russian invasion of Ukraine, calling it an affront to sovereign borders.

French Foreign Minister Jean-Noël Barrot told radio station France Inter he considers Greenland to be “a territory of the European Union.” He said the French government’s position is it is “out of the question that the European Union could let other nations of the world, whoever they may be, attack its sovereign borders”.

Trump has not brought up the prospect of military action over Greenland himself, but in response to a question from a journalist said he wouldn’t rule anything out. Indeed, Barrot said he didn’t actually believe Trump would use military force against a NATO ally but said such conversations were evidence the world was moving into a less secure era. He said: “If you’re asking me whether I think the United States will invade Greenland, my answer is no. But have we entered into a period of time when it is survival of the fittest? Then my answer is yes”.

Greenland’s relationship with the European Union is relatively complex. It joined the European Community in the 1970s alongside Denmark before it gained partial independence known as home rule. After getting some control over its own affairs, a referendum in Greenland in 1982 voted to leave what would later become the European Union over incompatibility between Brussels rules and Greenland’s domestic interests.

So while Greenland is not a member of the European Union, it is still an overseas territory of an EU member state, Denmark, and consequently an associate of the bloc. Whether the island could rejoin the EU has been a matter of sporadic discussion for years, but ultimately the reasons for leaving in the first place — the EU is damaging to the national fishing industry — remain fundamentally unchanged.

Le Figaro reports French government spokesman Sophie Primas has also spoken out on the possibility of the United States acquiring Greenland, denouncing it as “a form of imperialism”. She told the council of ministers on Wednesday: “More than ever, we must, with our European partners, be aware, move away from a form of naivety, protect ourselves, rearm ourselves”.

Unnamed European Union officials are “deeply disturbed by Trump’s comments”, states London’s strongly pro-Brussels Financial Times, stating the visit by Donald Trump Junior to Greenland this week has persuaded many the future President really is serious about acquisition, rather than just talking for effect.

Donald Trump Junior arrived in Greenland on Tuesday for a short visit, saying during his stay that anti-American sentiment in Danish media is fake news.

The United States has attempted to buy Greenland twice before, once in the 19th century and again at the end of the Second World War. Beyond its strategic importance in controlling the north Atlantic — denying the sea to Russian submarines, essential in case of war — Greenland is also very rich in minerals.