US Vice-President JD Vance says Greenland is critical for the defence of the US and the world against possible Russian or Chinese missile attacks - and that Europe and Denmark have not done a good job in securing the area.

Vance told Fox News that they had not only under-invested in Greenland's defences, but also failed to engage with President Donald Trump's argument over the issue.

US officials are actively discussing a potential offer to buy Greenland - a semi-autonomous Danish territory - the White House said on Wednesday, a day after suggesting military action to annex it to the US was also an option.

Denmark, a fellow Nato member, has warned this would spell the end of the alliance.

Both Greenland and Denmark have repeatedly stressed the island is not for sale.

Despite being the most sparsely populated territory, Greenland's location between North America and the Arctic makes it well placed for early warning systems in the event of missile attacks, and for monitoring vessels in the region.

The US already has more than 100 military personnel permanently stationed at its Pituffik base in Greenland's north-western tip - a facility that has been operated by the US since World War Two.

Under existing agreements with Denmark, the US has the power to bring as many troops as it wants to Greenland.

In recent years, there has also been increased interest in Greenland's natural resources - including rare earth minerals, uranium and iron - which are becoming easier to access as its ice melts due to climate change. Scientists think it could also have significant oil and gas reserves.

Vance emphasized that the missile defence infrastructure heavily relies on Greenland, stressing the island's strategic importance.

Concerns about the territory's future resurfaced after Trump's military actions against Venezuela. European leaders have expressed united support for Denmark, asserting that Greenland is not for sale and emphasizing sovereignty.