Protesters say authorities barred them from entering the sanctuary to attend an annual religious ceremony at a rebel monastery, where monks face eviction for fiercely opposing efforts to improve ties with the Vatican.
Five protesters broke through the police cordon and entered the grounds of Mount Athos, while dozens of others were turned back.
Police reported no injuries or arrests.
About 100 monks in the 1,000-year-old Esphigmenou Monastery have long been involved in a bitter fight with authorities at the all-male sanctuary and with the spiritual leader of the world’s Orthodox Christians, Ecumenical Patriarch Bartholomew I.
In a dispute spanning three decades, the zealot monks staunchly oppose efforts to improve relations between the Orthodox Church and the Vatican.
The Istanbul-based patriarch has declared them schismatic and ordered them out of the walled monastery — backed by an eviction order from Greece’s highest administrative court.
But the Esphigmenou monks have refused to leave the complex, and receive food and other assistance from religious supporters in other parts of Greece.
“We are raising the black flag of protest and say no to heresy,” said Father Isodoros, an Orthodox monk who took part in the protest. “We are being persecuted because we do not accept the betrayal of our faith.