Turkish President Recep Tayyip Erdogan attended Muslim prayers at Istanbul's Hagia Sophia on Friday, the first since the iconic place of worship in Istanbul was converted back into a mosque. 

First built as a cathedral in the Christian Byzantine Empire, the UNESCO World Heritage site in historic Istanbul was repurposed as a mosque in 1453, following the Ottoman conquest of Constantinople. 

In early July, Turkey's highest administrative court, the Council of State, reversed a decision made in 1934 by modern Turkey's founder, Mustafa Kemal Ataturk, to make the site into a museum. 

Following the ruling, Erdogan ordered that the place of worship be reopened for prayer. 

Watch: Turkey's historic monument reopens for first Muslim prayers

The decision has caused anger in the Christian community and particularly with NATO ally Greece, a majority Orthodox Christian country with historic links to the site.

During morning prayer, Erdogan recited a verse from the Koran, and later, the head of the state religious affairs agency, Ali Erbas, delivered the Friday sermon inside Hagia Sophia, holding a sword as a symbol of conquest.

"The reopening of Hagia Sophia ... is the return of a sacred place, which had embraced believers for five centuries, to its original function," Erbas told the congregation.

Despite the threat of COVID-19, large crowds gathered on Friday morning around the landmark, with several people reportedly spending the previous night there.

According to the president, there were 350,000 people in attendance in and around Hagia Sophia during Friday prayers, although the figures were unverified. 

While none of the leaders of the opposition parties participated, head of the right-wing Nationalist Movement Party (MHP), Devlet Bahceli, attended the prayers. 

He and Erdogan later visited the tomb of Sultan Mehmet II, who conquered the city in 1453.

Read more: Hagia Sophia: The future of one of the world's most iconic monuments remains uncertain

Politicization 

The government's decision to reconvert Hagia Sophia into a mosque is seen by analysts as an attempt to consolidate the Justice and Development Party's (AKP) nationalist and religious base as COVID-19 causes further problems for Turkey's ailing economy.

The move is also considered an attempt to solidify a long-term departure from Ataturk's legacy, with Erdogan professing nostalgia for the Ottoman empire as opposed to the founding father of modern Turkey's preference for secularism. 

The timing of the first prayer is also important, with Friday coinciding with the 97th anniversary of the Treaty of Lausanne, which set modern Turkey's borders after years of conflict with Greece and Western powers. The AKP has called for the treaty's revision in recent years.

The reconversion of Hagia Sofia comes at a time of strained relations between Turkey and its fellow NATO member Greece, as hydrocarbon exploration and drilling rights continue to cause friction in the eastern Mediterranean.  

Athens has criticized the conversion, calling it a provocation to the "entire civilized world."

"What is happening in [Istanbul] this day is not a show of force, but proof of weakness," Greek Prime Minister Kyriakos Mitsotakis said in a statement.

"Especially to us Orthodox Christians, Hagia Sophia today is in our hearts more than ever. It is where our heart beats."

Ankara has rejected such criticism in the name of sovereignty and says tourist visits to the site, of which there are 3.8 million each year, will still be allowed, as is the case with the majority of Istanbul's other mosques. 

Read more: EU condemns Turkish decision to convert Hagia Sophia back to mosque