Russian President Vladimir Putin, speaking after talks with Turkish President Tayyip Erdogan, said the agreement was that all heavy weapons be withdrawn from the zone, and that "radically-minded" rebels, including the Nusra front, would have to pull out of the zone.
Russian President Vladimir Putin said it would be 15km to 25km (9-15 miles) wide and come into force by 15 October.
Jan Egeland, adviser to the United Nations envoy for Syria, Staffan de Mistura, said: "Hope at long last for 3 million Syrian civilians in Idlib: Russia and Turkey agree on plan that may avert horrific war among displaced people".
Local media reported that the combats in Idlib province, near Turkey's north border, might cause a wave of refugees, so that issue was also discussed by the Turkish head of State.
Although opposition fighters have been gearing up for a possible confrontation with regime forces in their stronghold, the People's Protection Units (YPG) on Sunday said its forces would not join any battle in Idlib.
In rallies around Idlib in the last two weeks, protesters took to the streets to deny that the province is a hotbed of militants.
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"I think the Russians and the regime know if they attempted a ground invasion there would be grave losses on their side", Talib Talib, a commander of a rebel division that receives support from Turkey, told NPR.
The government forces kept sending reinforcements and military gears to a triangle of areas combining the northern countryside of Hama province in central Syria, the southern countryside of Idlib and the mountains of the Latakia province in northwestern Syria.
Speaking ahead of his meeting, Erdoğan said exchanging views on political, military and economic issues will strengthen both Turkey and Russian Federation.
"But together with Russian Federation, we will put our efforts into clearing those territories of radical elements", he said.
They also agreed that Idlib province will remain under the control of moderate rebel forces backed by Turkey - thereby nullifying the goal of President Bashar al Assad for a final offensive to united the country under his control.
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In response to Mr Trump, the study's authors have called it "the most accurate and unbiased estimate of excess mortality to date". On Thursday he claimed that the death toll in Puerto Rico was a Democratic ploy to " make me look as bad as possible ".
Relations between Turkey and Russian Federation, economy and energy issues, as well as regional and global issues, particularly Syria, were among the topics that were discussed.
Under a deal agreed with Russia, Turkey has already set up 12 so-called observation points inside Idlib aimed at monitoring a de-escalation of violence.
Idlib and surrounding areas is home to over 3 million Syrians, and an estimated 60,000 opposition fighters.
So in light of the recent development, the anticipated operation is believed to have been pushed back to a later time this month to give a chance for the efforts to separate the terror groups from other rebel factions, according to Maher Ihsan, a Syrian analyst.
Why it matters to Assad, Russia?
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