TURKISH President Recep Tayyip Erdogan is facing an international backlash over his decision to repurpose Istanbul’s Hagia Sophia museum as a mosque.

Mr Erdogan declared the iconic sixth-century building, which was originally a cathedral, a mosque and open for worship on Friday, following a court ruling that annulled the 1934 decision to turn it into a museum. He said it would remain open to visitors of all nationalities and religions.

World leaders and the heads of many Christian congregations expressed their dismay at the decision, warning that it would inflame tensions between Muslims and Christians much as Indian Prime Minister Narendra Modi’s determination to build a temple to the god Rama on the site on the site of the Babri Masjid mosque has between Muslims and Hindus in India. 

Patriarch Bartholomew of Constantinople said that “as a museum, the Hagia Sophia can function as a place and symbol of meeting, dialogue and peaceful coexistence of peoples and cultures,” noting that it had been a place of Christian worship for 900 years and a place of Muslim worship for 500 years.

And the move threatened to ignite a cultural war with Greece, which “condemns in the most intense manner the decision of Turkey to convert Hagia Sophia into a mosque. This is a choice which offends all those who also recognise the monument as a World Heritage Site,” according to a statement from the office of Prime Minister Kyriakos Mitsotakis. Mr Erdogan retorted that Greece had not “left standing” the Ottoman mosques erected on its territory when it was part of that empire.

Greece’s far-right Greek Solution party called for founder of the Republic of Turkey Kemal Ataturk’s house in Thessaloniki to be turned into a genocide museum in revenge, though it was Ataturk’s government which originally turned Hagia Sophia into a museum.

Hagia Sophia was built between 532 and 537 as the cathedral church of Constantinople by the Roman emperor Justinian, and was the largest church ever built until the completion of Seville Cathedral in 1520. As the seat of the patriarchs of Constantinople it was the principal church of Eastern Orthodox Christianity and was the scene of the Great Schism when a papal legate excommunicated patriarch Michael I Cerularius inside the building in 1054, sundering the eastern and western churches. It was converted into a mosque in 1453 following the Turkish conquest of Constantinople, but was closed in 1931 and reopened as a museum in 1935.