Prime Minister Rishi Sunak has ruled out a law change that would allow the UK to send back the disputed Elgin Marbles to Greece.
The famous sculptures, which once stood at the Parthenon in ancient Athens and are now at the British Museum, have been a source of contention between the two governments for more than 200 years.
The artefacts were removed from Greece by Lord Elgin in the early 19th century, when he was the British ambassador to the Ottoman Empire.
Speculation has grown in recent months that the sculptures could be sent back on a long-loan deal, so long as a change in legislation was approved by lawmakers.
However, these efforts were apparently rebuffed by Mr Sunak as he addressed reporters during a visit to San Diego in the US.
The 1963 British Museum Act prevents the institution giving away objects from its collection except in very limited circumstances.
Mr Sunak said that the UK had “cared for” the sculptures in the British Museum for generations and they were “shared with the world” at the London site.
“Our galleries and museums are funded by taxpayers because they are a huge asset to this country", he said.
“We share their treasures with the world, and the world comes to the UK to see them.
“The collection of the British Museum is protected by law, and we have no plans to change it.”
Last month, former chancellor George Osborne said a partnership was being explored between the two countries to facilitate a loan.
Mr Osborne, who is chairman of the British Museum, told the BBC that he was "reasonably optimistic" the law could be amended to allow the return of the Elgin Marbles.
He said he envisaged the marbles could be seen in London and in Athens, which would be a "win-win for Greece and for us".
But while decisions about the care and management of specific collections are a matter for the museum and its trustees, the government has made clear that long-term loans would not be part of its remit.