Last week, President Recep Tayyip Erdoğan announced that the sixth-century building would reopen as a mosque, shortly after a court decision annulled a 1934 decision converting it into a museum.
Erdoğan set the first prayers on June 24, citing preparations to make the domed compound, home to a world-famous mosaic depicting the face of an angel, compatible with Islamic prayers.
Erdoğan also said admission would be free of charge for visitors of all faiths, calling on foreign observers to "respect" the decision.