LONDON – British Prime Minister Boris Johnson told visiting Greek Premier Kyriakos Mitsotakis he can’t interfere to make the British Museum return the stolen Parthenon Marbles, and then both agreed it won’t affect relations between them.

Mitsotakis, who didn’t use a veto power when the United Kingdom was leaving the European Union to pressure for return of the treasures, instead raised the issue with Johnson, whose office said has no authority over the private museum.

That left Mitsotakis and Greece with no place to go apart from continuing a long-failed persuasion campaign, or try legal action although that approach has been sidelined in favor of diplomacy, negotiation and engaging allies ranging from celebrities to international supporters.

Mitsotakis’ call to Johnson came as Greece was nearing the end of a mostly-muted 200th anniversary celebration of independence from the four-century Ottoman Occupation, under whose rule Scottish diplomat Lord Elgin was allowed to remove half the marbles off the Parthenon from 1801-12.

Johnson said he “understood the strength of feeling of the Greek people” but stressed that decisions about the issue rest with the British Museum, where the marbles are held.

“The leaders agreed that this issue in no way affects the strength of the UK-Greece partnership,” Johnson’s office said. He earlier this year made similar statements and has refused to get involved.

The marbles – 17 figures and part of a frieze decorating the 2,500-year-old Acropolis monument – were taken by Elgin, the British Ambassador to the Ottoman Empire, which had no legal grounds to let him take them.

Britain maintains that Elgin acquired the sculptures legally when Greece was ruled by the Turks but the government said they were stolen and wants them returned for display in the new Acropolis Museum that opened in 2009.

Mitsotakis told Britain’s Daily Telegraph newspaper that “the marbles were stolen in the 19th Century, they belong in the Acropolis Museum and we need to discuss this issue in earnest,” but has left it at jawboning.

He earlier this year offered to loan the British Museum other Greek treasures if Greece could borrow and display the marbles it owns and didn’t raise the issue again until now.

Johnson’s spokesman stressed that the British Museum operates independently of the government and is free from political interference.

“Any decisions relating to the collections are taken by the museum’s trustees and any question about the location for the Parthenon sculptures is a matter for them,” he said.

The British Museum said on its website that Elgin’s actions were “thoroughly investigated by a Parliamentary Select Committee in 1816 and found to be entirely legal, prior to the sculptures entering the collection of the British Museum by Act of Parliament,” although Britain’s Parliament has no jurisdiction.

The museum’s trustees added they “firmly believe that there’s a positive advantage and public benefit in having the sculptures divided between two great museums, each telling a complementary but different story,” trying to defend the theft.

(Material from the Associated Press was used in this report)