ISTANBUL (Reuters) - About 200 Greek Orthodox Christians want to travel to Istanbul to try to hold mass at the former basilica of Hagia Sophia, defying Turkish law that bars religious services in what is now a museum.
A Turkish Foreign Ministry official said Ankara could stop the group from entering Turkey if they pose a security threat.
Prime Minister Tayyip Erdogan's government has lifted curbs on Christian worship at other sites under a EU-inspired drive to improve human rights. It has ruled out services at Hagia Sophia.
Turkish law from the 1930s has prevented both Muslims and Christians from formal worship at the monument, the greatest cathedral in Christendom for a millennium before invading Ottomans converted it into a mosque in the 15th century.
The U.S.-based group behind the attempt said it was on a mission to "re-establish Hagia Sophia as the holy house of prayer for all Christians of the world and the seat of Orthodoxy before the conquest of Constantinople by the Ottoman Turks in 1453."
Istanbul, formerly known as Constantinople, was the seat of the Greek Byzantine Empire until 1453. Hagia Sophia became a museum after the formation of modern secular Turkey in 1923.
Members are due to arrive in Istanbul on Friday.
The Foreign Ministry official said on condition of anonymity: "If an individual is known to pose a security problem, it's not possible for him to enter Turkey."
Culture Minister Ertugrul Gunay ruled out permission and said the group lacked good intentions. "Anyone can pray silently in this place but a group activity would pave the way for similar activities by members of other religions," Gunay said.
Turkey's population of 72 million is 99.9 percent Muslim.
In a letter to Erdogan, Chris Spirou, head of the group making the visit, said the issue was about religious freedom.
An official at the Greek Orthodox Patriarchate had said the group led by Spirou did not have its backing and said the event could make things harder for the patriarchate.
Turkey allowed Greek Orthodox Ecumenical Patriarch Bartholomew, spiritual leader of the world's 250 million Orthodox, to celebrate mass at a former monastery on the Black Sea coast last month for the first time since Greeks were expelled from most of Turkey in 1923.
Additional reporting by Tulay Karadeniz in Ankara