ARTICLE AD BOX
By Sam Francis
Political reporter, BBC News
Rishi Sunak's spokesman has said there is "no doubt" the Falkland Islands are British after Argentina's new president said it was time to "get them back".
Javier Milei, elected as Argentina's president on Sunday, said Buenos Aires had "non-negotiable sovereignty" over the islands.
And he vowed to get the islands back through "diplomatic channels".
But the UK prime minister's spokesman said the issue of sovereignty "was settled decisively some time ago".
Argentina has long claimed sovereignty over the islands, a British overseas territory in the south-west Atlantic Ocean. The two countries fought a war over the issue, after Argentine forces invaded the islands in 1982.
The Falklands, known in Argentina as the Malvinas, are about 8,000 miles from the UK and about 300 miles from mainland Argentina.
In a 2013 referendum, the people of the Falkland Islands voted 99.8% in favour of remaining a UK overseas territory.
Rishi Sunak's official spokesman said on Tuesday that the British government would continue to "proactively defend the Falkland Islanders right to self-determination".
'Malvinas are Argentine'
Earlier this year, Argentina pulled out of a co-operation deal signed in 2016 and has been pushing for talks on sovereignty.
In the agreement, Argentina and the UK pledged to "improve co-operation on South Atlantic issues of mutual interests".
Mr Milei said during a TV election debate: "What do I propose? Argentina's sovereignty over the Malvinas Islands is non-negotiable. The Malvinas are Argentine.
"Now we have to see how we are going to get them back. It is clear that the war option is not a solution.
"We had a war - that we lost - and now we have to make every effort to recover the islands through diplomatic channels."
In a newspaper interview with La Nacion, a daily newspaper in Argentina, he proposed that the UK hand over the Falklands to his South American country in a similar way to how Hong Kong was given back over to Chinese rule in 1997.
The populist politician, who has described himself as an anarcho-capitalist and is said to have lauded Margaret Thatcher - the British prime minister during the Falklands conflict - said the views of those living on the islands "cannot be ignored".
Defence Secretary Grant Shapps said it is "non-negotiable and undeniable" that the Falkland Islands are British.
In a social media post he said: "99.8% of islanders voted to remain British and we will always defend their right to self-determination and the UK's sovereignty."
In his tweets, Mr Shapps rejected any negotiation on the future of the Falklands, pointing out that the Royal Navy had redeployed HMS Forth to "protect the islands" in the southern hemisphere.
It follows a nine-month stint by HMS Medway patrolling the islands waters.