At least seven Greek monks have been injured in clashes over a disputed monastery in Mount Athos.
Fighting broke out between rebel Esphigmenou monks occupying a monastery office and a rival group of legally-recognised monks.
Police said the fight - in which fire extinguishers and crowbars were used as weapons - left seven needing treatment.
The rebel monks, who oppose closer ties between the Orthodox Church and the Vatican, have ignored orders to leave.
The fighting happened at the Esphigmenou group's representative office in the town of Karyes in Mt Athos.
Rebel abbot Methodius told the Associated Press news agency that his monks had been provoked.
Orthodox Patriarch Bartholomew I has told the rebel monks to leave
"We were attacked and had to respond," he said. "They should be ashamed to call themselves men of the cloth."
But the governor of Mount Athos, George Dalacouras, told the BBC's Malcolm Brabant that it was the other way round.
Mr Dalacouras said that the dispute was getting so bad that he feared someone would get killed soon, our correspondent adds.
Esphigmenou monastery has been the subject of a long-running dispute between Orthodox Church authorities and dissident monks.
The monks are bitterly opposed to the Orthodox Church's efforts to improve relations with the Roman Catholic Church, viewing relations between the two churches as tantamount to heresy.
The rebel monks have been occupying the site since 2003 and have ignored eviction orders from both the Orthodox Patriarch Bartholomew I and Greece's supreme court.
In October a Greek court gave two-year suspended custodial sentences to nine Esphigmenou monks for continuing their illegal occupation of the monastery offices.
Mount Athos is one of the holiest sites in Orthodox Christianity.