Turkey's president says his country does not have the "strength or capability" to host millions of more refugees from Idlib.
Recep Tayyip Erdogan said Friday that a call for terror groups in Idlib to lay down arms was a strong message to them and would help halt refugee flows.
"We have to take joint steps to prevent the migration, we need to be successful in the fight against terrorism," Erdogan said.
"Turkey is already sheltering 3 ½ million refugees (from Syria). The population of Idlib is 3 ½ million. Turkey doesn't have the strength or capability to host 3 ½ million more," he added.
Russian President Vladimir Putin says it is "unacceptable" to use civilians as a pretext to shield "terrorists" in Syria's rebel-held Idlib.
Speaking at the end of a trilateral summit with the leaders of Iran and Turkey Putin said Russia is worried about civilians in Idlib but said Russian finds it "unacceptable" when civilians are used a pretext to "shield terrorists" and target Syrian government positions.
Russia has been a key backer of Syrian President Bashar Assad and has indicated its support for Assad to regain control of Idlib which is the last remaining bastion of the opposition
Meanwhile, Iranian President Hassan Rouhani says "we have to force the United States to leave" Syria.
Rouhani did not elaborate on the comment, which he made while speaking about Idlib. America has some 2,000 troops in Syria.
Friday's summit may determine whether diplomacy halts any military action ahead of an anticipated offensive targeting the northwestern Syrian province.
Idlib province and surrounding areas are home to about 3 million people - nearly half of them civilians displaced from other parts of Syria. That also includes an estimated 10,000 hard-core fighters, including al-Qaida-linked militants.
Residents in Syria's northwestern Idlib province were holding mass rallies on Friday in the rebels' last bastion, protesting an imminent government offensive there and chanting against the country's ruler President Bashar Assad.
The Friday rallies came as Presidents of Iran, Turkey and Russia are meeting in Tehran to discuss the war in Syria. The summit may determine whether diplomacy halts any military action in Idlib and its surrounding areas, home to more than 3 million people. Nearly half of the area's residents are already displaced from other parts of Syria and have refused to reconcile with the Syrian government. The area also includes opposition fighters and some of Syria's most radical groups.
"Come on, leave Bashar!" hundreds of protesters chanted in Saraqeb, a town in eastern Idlib. "We will defend our revolution."