Iran, Russia, Turkey to decide fate of Syria's Idlib in Tehran summit

The presidents of Iran, Russia and Turkey - the main outside players in Syria's long war - meet in Tehran on Friday as rival factions in the rebel-held province of Idlib prepare for what could be the conflict's last great battle.

With Syrian government forces backed by Russian air power preparing an offensive against the insurgents in their last major stronghold, the United Nations has warned an assault could lead to a humanitarian catastrophe. Beyond that concern, the three leaders will be seeking to safeguard their own interests after investing heavily militarily and diplomatically in Syria.

"The battle for Idlib is going to be the final major battle," said Hilal Khashan, a political science professor at the American University of Beirut. "It will be waged irrespective of civilian casualties, even though they will make an effort to minimize it."

Tehran and Moscow have been President Bashar al-Assad's main backers and have helped him turn the course of the war against an array of opponents ranging from Western-backed rebels to Islamist militants. Turkey is a key opposition supporter. But the United States and other Western governments involved in the conflict will not be attending the summit.

Nonetheless, Russia's Vladimir Putin, Turkey's Tayyip Erdogan and Iran's Hassan Rouhani will be making decisions on what could be a turning point in a seven-year-old war which has killed more than half a million people and forced 11 million to flee their homes.