The British Prime Minister, Rishi Sunak canceled a scheduled meeting with Greek counterpart Kyriakos Mitsotakis on Tuesday amid a diplomatic dispute about the Parthenon Sculptures.

Greece has long maintained that the 2,500-year-old sculptures, removed by British diplomat Lord Elgin in the early 19th century and currently held in the British Museum, should be returned.

The statues, also known as the Elgin Marbles, have been a source of disagreement between the two nations for centuries.

Mitsotakis told the BBC on Sunday that renewed talks over a possible loan deal for the sculptures were not progressing quickly enough, and that the British Museum continuing to hold some of the artifacts while the rest remain in Athens is like cutting the “Mona Lisa in half.”

Sunak snubbed the Greek leader on the eve of their planned diplomatic meeting.

“The UK-Greece relationship is hugely important. From our work together in NATO, to tackling shared challenges like illegal migration, to joint efforts to resolve the crisis in the Middle East and war in Ukraine,” a Downing Street spokesperson said.

“I express my dismay that the British Prime Minister canceled our scheduled meeting just hours before it was due to take place,” Mitsotakis said in a Google-translated statement on Monday.

“Anyone who believes in the correctness and justice of their positions is never afraid of opposing arguments.”

The British government has always maintained that the marbles were legally acquired. A domestic law blocks the British Museum from permanently removing objects from its collection outside of particular circumstances, but does not prohibit a possible loan agreement.