Istanbul - President Recep Tayyip Erdogan on Saturday rejected worldwide condemnation over Turkey's decision to convert the Byzantine-era monument Hagia Sophia back into a Mosque, saying it represented his country's will to use its "sovereign rights".

Erdogan, who critics say is chipping away at the Muslim-majority country's secular pillars, announced Friday that Muslim prayers would begin on July 24 at the UNESCO World Heritage site.

In the past, he has repeatedly called for the stunning building to be renamed as a mosque and in 2018, he recited a verse from the Koran at Hagia Sophia. 

"Those who do not take a step against Islamophobia in their own countries ... attack Turkey's will to use its sovereign rights," Erdogan said during a ceremony he attended via video-conference.

A magnet for tourists worldwide, the Hagia Sophia was first constructed as a cathedral in the Christian Byzantine Empire but was converted into a Mosque after the Ottoman conquest of Constantinople in 1453.

Erdogan's announcement came after a top court cancelled a 1934 cabinet decision under modern Turkey's secularising founder Mustafa Kemal Ataturk to preserve the church-turned-Mosque as a museum.

The court ruled that "there are no provisions whatsoever in the convention (concerning the Protection of the World Cultural and Natural Heritage) that prevents ... the usage of the Hagia Sophia in accordance with domestic law." Erdogan then signed a presidential decree handing the control of the "Hagia Sophia Mosque" to Turkey's religious affairs directorate, Diyanet. "We made this decision not looking at what others say but looking what our right is and what our nation wants, just like what we have done in Syria, in Libya and elsewhere," the Turkish leader said Saturday.

- 'A blow to global Christianity' -

Erdogan went ahead with the plan despite appeals from NATO ally the United States and from Russia, with which Ankara has forged close relations in recent years.  After Friday's decision, hundreds gathered outside the iconic building and performed evening prayers. On Saturday, police had put up barriers around the Hagia Sophia.

"We wanted to come and visit Istanbul and the Hagia Sophia museum but unfortunately we realised that from today it is closed," said Renato Daleo, tourist from Italy.