Turkish President Recep Tayyip Erdogan has formally reconverted Istanbul's sixth-century Hagia Sophia into a mosque.
He declared it open to Muslim worship yesterday, hours after a high court annulled a 1934 decision that turned it into a museum.
The decision to reconvert Hagia Sophia - a former cathedral that was turned into a mosque after Istanbul's conquest by the Ottoman Empire and had served as a museum for 86 years - sparked dismay among Orthodox Christians.
But there was jubilation outside Hagia Sophia, where dozens of people who awaited the court's ruling outside chanted "Allah is great!" when the news came out.
Turkey's high administrative court threw its weight behind a petition brought by a religious group and annulled the 1934 cabinet decision that turned the site into a museum.
Within hours, Mr Erdogan signed a decree handing over Hagia Sophia to Turkey's Religious Affairs Presidency.
The president has demanded the hugely symbolic world heritage site should be turned back into a mosque despite widespread international criticism, including from the US and Orthodox Christian leaders.
The move could also deepen tensions with neighbouring Greece.
Cypriot Foreign Minister Nikos Christodoulides posted on his official Twitter account that Cyprus "strongly condemns Turkey's actions on Hagia Sophia in its effort to distract domestic opinion and calls on Turkey to respect its international obligations".
Nationalist and conservative groups have long been yearning to hold prayers at Hagia Sophia, which they regard as part of the Muslim Ottoman legacy. Others believe the Unesco World Heritage site should remain a museum, as a symbol of Christian and Muslim solidarity.
The group that brought the case to court had contested the legality of the 1934 decision by the modern Turkish republic's secular government ministers and argued the building is the personal property of Ottoman Sultan Mehmet II, who conquered Istanbul in 1453.
The court ruled Hagia Sophia is the property of a foundation managing the Sultan's assets and opened it up to the public as a mosque.
The Istanbul-based ecumenical patriarch Bartholomew I, warned in late June that the building's conversion into a mosque "will turn millions of Christians across the world against Islam".
Patriarch Kirill of Moscow, the leader of the Russian Orthodox Church, called for "prudence" and the preservation of the "current neutral status" for the Hagia Sophia, which he said was one of Christianity's "devoutly venerated symbols".
US State Secretary Mike Pompeo said last month that the landmark should remain a museum to serve as a bridge between faiths and cultures.
His comments sparked a rebuke from Turkey's Foreign Ministry, which said Hagia Sophia was a domestic issue of Turkish national sovereignty.
Mr Erdogan, a devout Muslim, has frequently used the Hagia Sophia issue, which sits at the heart of Turkey's religious-secular divide, to drum up support for his Islamic-rooted party.
Some Islamic prayers have been held in the museum in recent years and in a major symbolic move, Mr Erdogan recited the opening verse of the Quran in the Hagia Sophia in 2018.