Erdogan called on Putin and Rouhani to agree to a ceasefire in Idlib, saying such an accord would be a "victory" of their summit.
But regime backers Russian Federation and Iran have sworn to wipe out "terrorists" and Syrian President Bashar al-Assad has declared his determination to retake control of the entire country.
Russia, an ally of President Bashar al-Assad's regime, on Tuesday resumed air strikes on Idlib after a 22-day pause.
A Syrian woman sits on a straw mat next to children outside a tent at a camp for displaced civilians fleeing from advancing government forces near the village of Sarman in the rebel-held northwestern Idlib province, September 1, 2018. Idlib is the last major redoubt of the insurgents.
The province is home to some three million people - around half of them displaced from other parts of the country, according to the United Nations.
Neighbouring Turkey, which has long backed Syrian rebels, fears the assault could prompt an influx of desperate Syrians attempting to find safety on its territory. They appealed to world leaders to "urgently work together to avoid this horrific scenario".
America's ambassador to the UN, Nikki Haley, has warned any military offensive in Idlib "would be a reckless escalation".
For Russia and Iran, both allies of the Syrian government, retaking Idlib is crucial to complete what they see as a military victory in Syria's civil war after Syrian troops recaptured almost all other major towns and cities, largely defeating the rebellion against Assad. They are also due to hold a press conference.
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As the conflict approaches its endgame, Iran, Turkey and Russian Federation are seeking to safeguard their own interests after investing heavily militarily and diplomatically in Syria.
Neighbouring Turkey has limited sway over the jihadists who control an estimated 60% of the province but it backs rebel groups there and has 12 military "observation points" across the province.
"The Trump Administration and the worldwide community have made it clear that there is no military solution to the Syrian conflict", Haley told the Council, which was to hold another meeting Friday on the crisis in Idlib. "Peace must return to Syria", said spokeswoman Maria Zakharova in comments reported by Russian agencies.
The summit between Iranian President Hassan Rouhani, Russian President Vladimir Putin and Turkish President Recep Tayyip Erdogan may determine whether diplomacy halts any military action.
Her Iranian counterpart, Bahram Ghassemi, assured Damascus of Tehran's support and willingness to "continue its role as adviser and help" for the Idlib campaign. Syrian government forces resumed shelling of rebels there.
Turkish President Recep Tayyip Erdogan said Friday at the meeting that an attack on Idlib would result in a disaster and massacre, and that millions of people would be moving towards the Turkish border in the case that an attack took place. "Millions will be coming to Turkey's borders because they have nowhere to go".
Turkey, Russia and Iran are guarantor countries of de-escalation zones in Syria.