Greenland and the Antarctic are “not for sale”, Emmanuel Macron has declared in a thinly-veiled rebuke to Donald Trump.

The US president is reportedly costing up the price of taking over Greenland and planning to offer more cash than Denmark pays to the autonomous territory.

But at the opening of the UN Ocean Conference in Nice, on the French Riviera, Mr Macron said: “The abysses are not for sale, and neither is Greenland, nor is Antarctica or the high seas.”

The French president also told world leaders that it was a “necessity” for nations to impose a moratorium on deep-sea mining.

“I think it’s madness to launch predatory economic action that will disrupt the deep seabed, disrupt biodiversity, destroy it. The moratorium on deep-seabed exploitation is an international necessity,” he told the gathering.