Thousands gather for 1st prayers after Hagia Sophia's controversial conversion into mosque

Thousands of worshippers gathered at the Hagia Sophia in Istanbul for Friday prayers, after the controversial move by the Turkish government to re-convert the museum into a functioning mosque.

President Recep Tayyip Erdogan was taking part in the first prayers to be held in the building in 86 years. Huge crowds of worshippers were seen gathering outside the building in Istanbul, many of whom had camped out overnight.

Earlier this month, Erdogan formally declared that the iconic Hagia Sophia would be used as a mosque, after a Turkish court annulled a decision made in the 1930s that had converted it into a museum. As a museum, the Hagia Sophia was seen as a symbol of the secular nature of modern Turkey. Erdogan has long been accused of seeking to reshape Turkey along Islamic lines.

The Turkish government has said that the Hagia Sophia will still be open for visitors.

The Hagia Sophia was once one of the most revered cathedrals in the Christian Orthodox tradition, and the decision to convert it into a mosque attracted widespread criticism from political and religious leaders around the world. The Hagia Sophia was converted into a mosque after the Ottoman Empire's conquest of Istanbul in the 15th century.

International criticism is pouring in. Catholic Cardinal Timothy Dolan of New York joined in a statement with the Greek Orthodox Archbishop of America saying they "lament and decry" the decision.

UNESCO expressed its "deep regret' at the Turkish government's decision, saying it was made "without prior discussion."

"Hagia Sophia is an architectural masterpiece and a unique testimony to interactions between Europe and Asia over the centuries," UNESCO Director-General Audrey Azoulay said after the conversion was announced. "Its status as a museum reflects the universal nature of its heritage, and makes it a powerful symbol for dialogue."

The reconversion also attracted criticism from the U.S. State Department and the European Union. In response, the Turkish Foreign Minister said the decision was "a matter that concerns Turkey's sovereign rights."

The move will undoubtedly increase tensions between Greece and Turkey.

Perhaps the most significant international criticism of the move is coming from Greece, where a large number of Orthodox Christians live, and the Greek community. The Greek Orthodox Archdiocese of America declared Friday a "day of mourning." Greece's Minister of Culture, Lina Mendoni, described Erdogan's decision as an "open provocation to the civilised world."

"Hagia Sophia is one of the most important human creations, one of the most important monuments, representing many universal values," she said on Wednesday. "These universal values are in danger of being lost through the conversion of the monument into a mosque."