This aerial picture taken on June 28, 2020 in Istanbul shows Hagia Sophia museum in Istanbul. (OZAN KOSE / AFP)

ANKARA - A Turkish court on Thursday heard a case aimed at converting Istanbul's sixth century Hagia Sophia back into a mosque and will announce its verdict within 15 days, a lawyer said, on an issue which has drawn international expressions of concern.

The government decision to turn the mosque into a museum was made in 1934 in the early years of the modern secular Turkish state founded by Mustafa Kemal Ataturk

President Tayyip Erdogan has proposed restoring the mosque status of the UNESCO World Heritage Site, a building at the heart of both Christian Byzantine and Muslim Ottoman empires and today one of Turkey's most visited monuments.

The government decision to turn the mosque into a museum was made in 1934 in the early years of the modern secular Turkish state founded by Mustafa Kemal Ataturk. The court case disputes the legality of that conversion.

US Secretary of State Mike Pompeo on Wednesday urged Turkey to let Hagia Sophia remain a museum, while the spiritual head of the world's Orthodox Christians warned its conversion to a mosque would sow division.

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Hagia Sophia was the foremost church in Christendom for 900 years and then one of Islam's greatest mosques for 500 years after the Ottoman conquest of Istanbul.

People visit Hagia Sophia museum on June 26, 2020 in Istanbul. (OZAN KOSE / AFP)

Ecumenical Patriarch Bartholomew, the spiritual head of some 300 million Orthodox Christians worldwide and based in Istanbul, said converting it to a mosque would disappoint Christians and would "fracture" East and West.

Turkish groups have campaigned for years for Hagia Sophia's conversion into a mosque and Erdogan, a pious Muslim, backed their call ahead of local elections last year.

Many Turks argue that mosque status would better reflect the identity of Turkey as an overwhelmingly Muslim country, and recent polls have shown that most Turks support a change.