President Donald Trump says the US needs to "own" Greenland to prevent Russia and China from doing so.

"Countries have to have ownership and you defend ownership, you don't defend leases. And we'll have to defend Greenland," Trump told reporters on Friday, in response to a question from the BBC.

We will do it "the easy way" or "the hard way", he added. The White House said recently the administration is considering buying the semi-autonomous territory of fellow Nato member Denmark, but it would not rule out the option of annexing it by force.

Denmark and Greenland say the territory is not for sale. Denmark has said military action would spell the end of the trans-Atlantic defence alliance.

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 president has repeatedly said that Greenland is vital to US national security, claiming without evidence that it was "covered with Russian and Chinese ships all over the place".

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.

But speaking to reporters in Washington, Trump said a lease agreement was not good enough.

"Countries can't make nine-year deals or even 100-year deals," he said, adding that they had to have ownership.

"I love the people of China. I love the people of Russia," Trump said. "But I don't want them as a neighbour in Greenland, not going to happen."

"And by the way Nato's got to understand that," the US president added.

Denmark's Nato allies - major European countries as well as Canada - have rallied to its support this week with statements reaffirming that "only Denmark and Greenland can decide on matters concerning their relations".

Stressing they were as keen as the US on Arctic security, they have said this must be achieved by allies, including the US, "collectively".

They also called for "upholding the principles of the UN Charter, including sovereignty, territorial integrity and the inviolability of borders".

Concerns over the future of the territory resurfaced after Trump's use of military force against Venezuela on Saturday to seize its president, Nicolás Maduro.

Trump previously made an offer to buy the island in 2019, during his first presidential term, only to be told it was not for sale.

US Secretary of State Marco Rubio is to hold talks with Denmark next week.

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.

In a joint statement on Friday night, Greenland's party leaders, including the opposition, reiterated their call for the "US's disregard for our country to end".

"We do not want to be Americans, we do not want to be Danes, we want to be Greenlanders," they said. "The future of Greenland must be decided by the Greenlandic people."