Turkish President Recep Tayyip Erdogan has said Istanbul’s Hagia Sophia, a Byzantine-era cathedral that was turned into a mosque and now serves as a museum, could be reconverted into a mosque.

Mr Erdogan spoke during a television interview on Sunday ahead of Turkey’s March 31 local elections.

The former Byzantine cathedral was converted into a mosque after the Ottoman conquest of Istanbul in 1453.

Gallipoli centenary commemorations
Turkish President Recep Tayyip Erdogan (Niall Carson/PA)

Turkey’s secular founder turned the structure into a museum in 1935 that attracts millions of tourists each year.

There have been increasing calls for the government to convert the symbolic structure back into a mosque.

Those calls were amplified by reports that the gunman who killed Muslim worshippers in New Zealand left a manifesto saying the Hagia Sophia would be “free of minarets”.

Mr Erdogan himself recited prayers inside the Hagia Sophia last year.

The suggestion that Hagia Sophia could be turned into a mosque drew ire in Greece.

Hagia Sophia
Protesters calling for the Hagia Sophia to be reconverted into a mosque (Lefteris Pitarakis/AP)

“It is not only a great temple of Christendom, the largest for many centuries, it also belongs to humanity.

“It has been recognised by Unesco as part of our global cultural heritage,” Greek foreign minister George Katrougalos said.

“So any questioning of this status is not just an insult to the sentiments of Christians, it is an insult to the international community and international law.”

“We want to hope that the correct statements of March 16 by the Turkish leadership will be valid and there will be no change of this status,” he added, in reference to a speech by Mr Erdogan when he ruled out its conversation into a mosque.