The Greek prime minister has hit out at the British Museum's loan of one of the Elgin Marbles to Russia, calling it an "affront" to his country's people.
Antonis Samaras said the sculptures, which have been loaned for the first time to the State Hermitage Museum in St Petersburg, had been "looted" from Athens.
The river god Ilissos is going on show in Russia until mid-January, despite tensions over Ukraine and a long-running dispute with Greece over ownership of the marbles.
The headless statue is one of a number of marble treasures taken from the Parthenon and sold to the British Museum by Scottish diplomat Lord Elgin in the early 19th century.
Greece maintains the Elgin Marbles were removed illegally during the country's Turkish occupation and should be returned for display in a new Athens museum - which the British Museum and the Government reject.
The British Museum's director Neil MacGregor indicated that he would be willing to consider a similar loan of a statue to Greece - but only if the authorities there promised to return it to London.
Mr MacGregor said he hoped the Greek government would be "delighted" that the sculpture would be on display to a new audience.
But Mr Samaras said: "The decision by the British Museum to give out on loan one of the Parthenon sculptures for exhibit in St Petersburg is an affront to the Greek people.
"The British argument held until recently - that the Parthenon Marbles cannot be moved - is no longer valid; just as the existence of the new Acropolis Museum invalidated the other British argument that there was no appropriate space for exhibiting the sculptures.
"The Parthenon and its marbles have been looted. The sculptures are priceless.
"We Greeks are one with our history and civilization, which cannot be broken up, loaned out, or conceded."
It is the first time one of the British Museum's Parthenon sculptures, which represents about a third of the original decoration of the temple, has been requested for loan
They have never previously left the museum except during wartime.
Explaining the loan to the Hermitage at a time of tension between the West and Vladimir Putin, Mr MacGregor said in a blog on the British Museum website: "The trustees have always believed that such loans must continue between museums in spite of political disagreements between governments."
In October, human rights barrister Amal Clooney called on Britain to give up its "intransigence" and start talks with Greece on the return of the Elgin Marbles.
The Lebanese-born barrister and wife of the Hollywood film star George Clooney has been advising the Greek government on how it can best pursue its claims to win back the ancient artefacts.
UNESCO, the United Nations' cultural organisation, has also called on Britain to enter into a process of mediation with the Greeks in order to settle the 200-year-old dispute.
The British Museum says it is holding the marbles, and its other treasures, "in trust for the nation and world" and insists their legal status is clearly defined in the British Museum Act.
