Muslim prayers will echo on Friday from the iconic Hagia Sophia in Istanbul for the first time in 86 years after its reconversion into a mosque earlier this month.

Recep Tayyip Erdogan, who joined hundreds of worshippers, said last year it had been a “very big mistake” to convert the Hagia Sophia into a museum.

On July 10 he controversially declared the nearly 1,500-year-old monument open to Muslim worship after a top court ruled the building’s conversion to a museum by modern Turkey’s founding statesman was illegal.

The UNESCO World Heritage Site was built as a cathedral during the reign of Byzantine emperor Justinian I in 537 but converted into a mosque after the Ottoman conquest of Constantinople in 1453.

It was designated a museum in a key reform of the post-Ottoman authorities under the modern republic"s founder Mustafa Kemal Ataturk.