Turkish President Recep Tayyip Erdogan is hosting more than 30 heads of state and government from Islamic countries in Istanbul for a summit aimed at overcoming differences in the Muslim world.
The two-day summit of the Organisation of Islamic Cooperation (OIC) got under way at 06:30 GMT on Thursday with a speech by Erdogan.
The summit will end on Friday with a news conference held by Erdogan.
Prominent guests at the meeting include Saudi King Salman bin Abdulaziz Al Saud and Iranian President Hassan Rouhani, whose countries find themselves on opposing sides in the Syria and Yemen conflicts.
Turkey has said it wants to use the meeting to narrow differences between the world's estimated 1.7 billion Muslims.
However, the gathering risks being overshadowed by disputes on issues ranging from Syria to Yemen.
There is a security lockdown around the summit venue in Istanbul, the former capital of the Ottoman Empire from where the Ottoman sultans for centuries ruled Muslims from the Balkans to Arabia.
While the summit marks one of the most significant gatherings of heads of state for years in Istanbul, some prominent leaders such as Jordan's King Abdullah and Egyptian President Abdel Fattah el-Sisi will be notable by their absence.
|The gathering risks being overshadowed by disputes on issues ranging from Syria to Yemen [Reuters]
Turkey's relations with Egypt have still not recovered from the 2013 overthrow of President Mohamed Morsi, a close ally of Turkey, while ties with Jordan are being tested by differences over Syria.
Mevlut Cavusoglu, Turkish foreign minister, said the summit was being held at a time when "the Islamic world is experiencing many disputes within itself.
"Fratricidal conflict causes great pain. Sectarianism divides the ummah," he told OIC foreign ministers on Tuesday, using the Arabic world for the Muslim community.
"Hopefully, this summit will pave the way for healing some wounds."
But Turkey's own policies in the Middle East have been facing critical scrutiny, with several Muslim states objecting to the backing by its government of rebels in Syria.
The run-up to the summit saw a visit by Salman to Ankara which marked the visible improvement in ties between Turkey and Saudi Arabia since he came to the throne in 2015.
Erdogan went to Ankara's Esenboga airport to personally welcome Salman on the tarmac and then gave him Turkey's highest honour for a foreign leader.
|Turkey wants to use the Istanbul meeting to narrow differences between the world's estimated 1.7 billion Muslims [EPA]
Salman landed in Istanbul on Wednesday to find cars waiting on the tarmac to transport him and his delegation to their hotel by the Bosphorus.
Saudi Arabia and Turkey both believe the toppling of President Bashar al-Assad is the key to solving the Syrian conflict and back rebel groups fighting his government.
However, Turkey needs to tread carefully in its alliance with Saudi Arabia, which is also overwhelmingly Sunni Muslim, so it is not seen as a sectarian union aimed at mainly Shia Iran.