Despite international condemnation, Turkish President Recep Tayyip Erdoğan led the first Muslim prayer in Hagia Sophia in 86 years on Friday.
Thousands of people attended the first prayer in and around Hagia Sophia.
The prayers began with Erdogan reading from the Quran, after which the call to prayer was heard from the four minarets around the monument.
Due to the coronavirus pandemic, only about a 1,000 people were allowed inside but many more crowded outside and failed to observe safety measures, such as social distancing and masks.
Greece and the world have strongly denounced the conversion of Hagia Sophia into a mosque.
On Friday, July 24, the day of mourning, the Greek Foreign Affairs Ministry called the conversion "a blow to humanity's cultural heritage."
The ministry underlined that changing the monument's museum status is a violation of Turkey's obligations under the 1972 UNESCO Convention, an action which "casts a heavy shadow over its image."
The statement also highlighted that altering the monument entails significant risks for both the building's integrity and its interior decoration, "including the mosaics and other works of art."
On his part, Greek Prime Minister Kyriakos Mitsotakis stressed that Friday's event at Hagia Sophia was not a display of strength but a proof of weakness.
"Especially for us Orthodox Christian Greeks, Hagia Sophia is today more than ever...where our heart beats. Converting sorrow into strength, calmness and unity, because Hagia Sophia exists precisely because it unites us all, calling on us to only look up," he said.
Similarly, SYRIZA leader Alexis Tsipras noted that the conversion cannot "distort or wipe out its history and its ecumenical symbolism."
"The conversion of Hagia Sophia museum into a temple, on the anniversary of the Treaty of Lausanne signing, marks for Turkey another step away from universal values that serve as underpinnings for peace and mutual respect in our region, while it undermines inter-religious dialogue in a fundamental way," the main opposition leader said.