Ankara: A Turkish court annulled on Friday a 1934 government decree turning Istanbul's Hagia Sophia into a museum, paving the way for the building's conversion back into mosque despite international warnings against such a move.

President Tayyip Erdogan had proposed restoring the mosque status of the UNESCO World Heritage Site, a focal point of both the Christian Byzantine and Muslim Ottoman empires and now one of the most visited monuments in Turkey.

Also read: Undoing Atatürk: What Erdoğan Gains in Turning Istanbul’s Hagia Sophia Into a Mosque Again

The United States, Greece and church leaders were among those to express concern about changing the status of the huge 6th Century building, converted into a museum in the early days of the modern secular Turkish state under Mustafa Kemal Ataturk.

"It was concluded that the settlement deed allocated it as a mosque and its use outside this character is not possible legally," the Council of State, Turkey's top administrative court, said in a ruling.

"The cabinet decision in 1934 that ended its use as a mosque and defined it as a museum did not comply with laws," it said.

The association which brought the court case, the latest in a 16-year legal battle, said Hagia Sophia was the property of the Ottoman leader who captured the city in 1453 and turned the already 900-year-old Byzantine church into a mosque.

The Ottomans built minarets alongside the vast domed structure, while inside they added huge calligraphic panels bearing the Arabic names of the early Muslim caliphs alongside the monument's ancient Christian iconography.

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