VATICAN CITY — Pope Francis said on Sunday that he is "deeply pained" over the decision by Turkey to change the status of Hagia Sophia — which was originally built in Istanbul as a Christian cathedral — from a museum to a mosque. 

In a very brief, improvised remark, Francis, speaking from his studio window overlooking St. Peter's Square, noted that the Catholic Church marked Sunday as International Day of the Sea. "And the sea brings me a little far away with my thought: to Istanbul," the pontiff said. "I am thinking of St. Sophia and I am deeply pained." 

Francis said no more but was clearly referring to the move by Turkish President Recep Tayyip Erdogan to formally convert the monumental building back into a mosque. The colossal Santa Sophia cathedral was turned into a mosque after the Ottomans conquered the city in 1453. The Turkish secular government in 1934 decided to make it a museum.

The pope, who heads the Roman Catholic church, is adding his voice to strong objections a day earlier by the head of the Geneva-based World Council of Churches. That organization described its "grief and dismay" in noting that Hagia Sophia has been "a place of openness, encounter and inspiration for people from all nations." The council's membership comprises Protestant, Orthodox and Anglican churches. 

Erdogan declared the monument open for Muslim worship after a high court annulled the 1934 government decision.