Turkey's president led hundreds of worshippers yesterday at a reconverted Istanbul mosque for the first Muslim prayers there in 86 years.
President Recep Tayyip Erdogan fulfilled 'the dream of [his Islam-oriented] youth' and read from the Quran to begin the prayers inside the historic Hagia Sophia.
The Istanbul landmark served as one of Christendom's most significant cathedrals, a mosque and a museum before its conversion back into a Muslim place of worship.
Thousands of other Muslim faithful came from across Turkey and quickly filled specially designated areas outside of the Byzantine era monument to join in the inaugural prayers. Many others were turned away, while Orthodox Christian church leaders in Greece and the United States announced a "day of mourning" over Hagia Sophia's return as a mosque.
The head of Turkey's religious authority, Ali Erbas, led the ceremony and prayed that Muslims would never again be "denied" the right to worship at the internationally celebrated sixth century structure.
As many as many as 350,000 people took part in yesterday's prayers, the president said.
Brushing aside international criticism, Mr Erdogan issued a decree restoring the iconic building as a mosque earlier this month, shortly after a Turkish high court ruled that the Hagia Sophia had been illegally made into a museum more than eight decades ago.
The structure, listed as Unesco World Heritage site, has since been renamed The Grand Hagia Sophia Mosque.
The move sparked dismay in Greece, the US and among Christian churches who had called on Mr Erdogan to maintain it as a museum as a nod to Istanbul's multi-religious heritage and the structure's status as a symbol of Christian and Muslim unity. Pope Francis expressed his sadness.
Built in 537, Hagia Sophia was turned into a mosque with the 1453 Ottoman conquest of Istanbul.
Mustafa Kemal Ataturk, the founding leader of the secular Turkish republic converted the structure into a museum in 1934.
Religious and nationalist groups in Turkey have long yearned for the nearly 1,500-year-old edifice to be reverted into a mosque.
"This is Hagia Sophia breaking away from its captivity chains. It was the greatest dream of our youth," Mr Erdogan said last week. "It was the yearning of our people and it has been accomplished."
In neighbouring Greece, bells tolled and flags flew at half-mast at hundreds of churches across the country in protest at the decision.
"Today is a difficult day - a shadow hangs over us with the transformation of Hagia Sophia into a mosque - something that genuinely shocks Christians all over the world and not only Greeks," Greek government spokesman Stelios Petsas said in an interview with private channel Open TV.
In New York, the Greek Orthodox Archdiocese of America called the inaugural prayers a "cultural and spiritual misappropriation and a violation of all standards of religious harmony and mutual respect."
Archbishop Elpidophoros of America held a meeting with US President Donald Trump in Washington on Thursday to discuss concerns over the reconversion.