ISTANBUL (Reuters) - Turkey and Greece exchanged harsh words on Saturday over the conversion of Istanbul’s Hagia Sophia into a mosque, a day after Islamic prayers were held at the ancient site for the first time in nine decades.

Greek criticism of the move to convert the site from a museum has been scathing, underlining tense ties between Greece and Turkey. Church bells tolled in mourning across Greece on Friday as Turkish President Tayyip Erdogan joined prayers at the building.

“Greece showed once again its enmity towards Islam and Turkey with the excuse of reacting to Hagia Sophia Mosque being opened to prayers,” Turkish Foreign Ministry spokesman Hami Aksoy said in a written statement on Saturday.

The ministry strongly condemned hostile statements by the Greek government and parliament members to stir up the public, and the burning of a Turkish flag in the Greek city of Thessaloniki, it said.

Hagia Sophia was opened to prayer as a mosque in line with the will of the Turkish people and belonged to Turkey like all cultural assets in the country, it added.

The Greek Foreign Ministry responded with its own statement, saying “the international community of the 21st century is stunned to observe the religious and nationalist fanatic ramblings of today’s Turkey.”

Friday’s ceremony sealed Erdogan’s ambition to restore Muslim worship at the site, which most Greeks view as central to their Orthodox Christian religion.

On Friday, Greek Prime Minister Kyriakos Mitsotakis called Turkey a “troublemaker”, and the conversion of the site an “affront to civilisation of the 21st century”.

Greece and Turkey disagree on a range of issues from airspace to maritime zones and ethnically split Cyprus. This week they also exchanged barbs over the delimitation of their continental shelves in the eastern Mediterranean, an area thought to be rich in natural resources.