A decision by President Recep Tayyip Erdogan, published in the country’s Official Gazette, said Istanbul’s Church of St Saviour in Chora, known as Kariye in Turkish, was handed to Turkey’s religious authority, which would open up the structure for Muslim prayers.
Like the Hagia Sophia, which was a church for centuries and then a mosque for centuries more, it had operated as a museum for decades before Mr Erdogan ordered it restored as a mosque.
It was not immediately known when the first prayers would be held there.
The church, situated near the ancient city walls, is famed for its elaborate mosaics and frescoes.
The structure served as a mosque during the Ottoman rule before being transformed into a museum in 1945.
A court decision last year cancelled the building’s status as a museum, paving the way for Friday’s decision.
And as with the Hagia Sophia, the decision to transform the Chora back into a mosque is seen as geared to consolidate the conservative and religious support base of Mr Erdogan’s ruling party at a time when his popularity is sagging amid an economic downturn.
Greece’s foreign ministry strongly condemned the move, saying that Turkish authorities “are once again brutally insulting the character” of another UN-listed world heritage site.
“This is a provocation against all believers,” the Greek ministry said in a statement.
“We urge Turkey to return to the 21st century, and the mutual respect, dialogue and understanding between civilisations.”
Elpidophoros, the Greek Orthodox archbishop of America, wrote on Twitter: “After the tragic transgression with Hagia Sophia, now the Monastery of Chora, this exquisite offering of Byzantine culture to the world!”
Several Istanbul residents rushed to the building, some hoping to hold prayers there, Turkey’s state-run Anadolu Agency reported.
“Like the Hagia Sophia, this is an important mosque for Muslims,” the agency quoted Istanbul resident Cuma Er as saying.
“We came here to pray after we learned about the decision.
“But we have been told that it has not yet been opened for prayers.
“We are waiting for the opening.”
Last month, Mr Erdogan joined hundreds of worshippers for the first Muslim prayers in Hagia Sophia in 86 years, brushing aside the international criticism and calls for the monument to be kept as a museum in recognition of Istanbul’s multi-faith heritage.
As many as 350,000 took part in the prayers outside the structure.