Turkey's religious affairs authority has said Christian images in the famous Hagia Sophia will be concealed.
Its statement comes as the country's officials decided to transform Istanbul's landmark structure from a museum to a mosque. It used to be a cathedral before becoming a mosque, and then a museum.
The officials who are preparing the site for Muslim worship said the Christian depictions inside are no obstacle to Muslim prayers.
They added however, that the figures would need to be covered with curtains or through other means during the prayers, in line with Islamic traditions that prohibit such representations.
Meanwhile, Turkey's foreign minister has scolded the European Union over its condemnation of the decision to convert Hagia Sophia from a museum to a mosque, saying the matter is an issue of national sovereignty.
Last week, Turkey cancelled the sixth-century former cathedral-turned-mosque's 86-year status as a museum and said it would open for Muslim worship as of 24th July.
The decision sparked criticism in the United States, Greece, and other Western countries as well as from Orthodox Christian leaders.
Pope Francis expressed sadness over the move.
EU foreign ministers, holding their first face-to-face meeting in months on Monday, declared that they "condemned" the decision.
EU foreign affairs chief Josep Borrell said there was "broad support to call on the Turkish authorities to urgently consider and reverse this decision".
Asked to comment on the EU criticism, foreign minister Mevlut Cavusoglu told a joint news conference with his visiting Maltese counterpart: "We reject the word 'condemnation'."
"This is a matter that concerns Turkey's sovereign rights," he said.
He argued that there were several mosques in EU-member Spain that had been converted into churches.
Turkish President Recep Tayyip Erdogan, meanwhile, described the 1934 decision by the Turkish Republic's secular, founding leaders that converted Hagia Sophia from a mosque into a museum as a mistake.
"We are rectifying a mistake. It's as simple as that," Mr Erdogan said in a televised address, following a weekly Cabinet meeting.
Mr Erdogan maintained that the criticisms levelled against Turkey over Hagia Sophia's return to a mosque were a "pretext" for enmity toward Turkey and Islam.
He also said his country was determined to preserve the structure's qualities as a cultural heritage.
On Tuesday, Greece again expressed dismay at Turkey's decision.
"This decision is certainly painful to us as Greek Orthodox Christians but it also hurts us as citizens of the world," said Greek prime minister Kyriakos Mitsotakis.
"This is not a Greek-Turkish issue, it is not even a Euro-Turkish issue, it is global.
"It is a universal issue."
Mr Mitsotakis added: "With this setback, Turkey is choosing to sever ties with the Western world and its values.
"It abandons a cultural direction of many centuries, preferring introversion.
"And it wraps with an artificial mantle of strength over its weakness."