The presidents of Russia and Turkey have agreed to create a demilitarized buffer zone in Syria's Idlib region to separate government and rebel forces.
President Vladimir Putin said that the buffer zone would be 15 to 25 kilometers wide and come into force by October 15.
This would entail a "withdrawal of all radical fighters" from Idlib including the Al-Qaeda-linked Al-Nusra Front, Putin said after more than four hours of talks with his Turkish counterpart, Recep Tayyip Erdogan, in the Russian city of Sochi on September 17.
The two leaders also agreed on the withdrawal of "heavy weaponry from this zone," including tanks, multiple-launch rocket systems, and rocket launchers belonging to all armed groups, Putin added.
Speaking at a joint news conference, Erdogan said the two countries would carry out coordinated military patrols on the borders of the buffer zone.
"The opposition will continue to remain in the areas where they are. In return, we will ensure that the radical groups, which we will determine with Russia, will not operate in the area under discussion," Erdogan said.
The meeting in the Russian Black sea resort city of Sochi comes 10 days after a summit between Vladimir Putin, Recep Tayyip Erdogan, and their Iranian counterpart, Hassan Rohani, failed to produce a compromise in a bid to avert an expected Syrian government offensive in Idlib Province, which the Turkish president has warned would ignite a "bloodbath."
Moscow and Tehran have given Syrian President Bashar al-Assad crucial support throughout the war, which began with a government crackdown on protesters in March 2011.
The three allies have been pressing ahead with the Idlib offensive, saying they want to put an end to what they call the last main "terrorist" stronghold in Syria.
However, Turkey is backing rebel groups and it fears that a large-scale assault on Idlib, which lies on its southern border, could trigger a massive flow of refugees onto its soil.
The country is already home to more than 3 million Syrians who have fled the war.
Idlib Province is the Syrian opposition's last major stronghold and it is held by an array of rebels.
The most powerful is Tahrir al-Sham, a merger of Islamist groups dominated by the former Al-Nusra Front -- an Al-Qaeda affiliate until 2016.
Other Islamists, and groups fighting as the Free Syrian Army banner, are now gathered with Turkish backing under the banner of the National Front for Liberation.
Neither Putin not Erdogan explained how they planned to differentiate "radical" rebels from other anti-Assad groups.
It was also not immediately clear how much of the city of Idlib fell within the buffer zone.
Earlier, Turkey's Hurriyet daily quoted Erdogan as saying Ankara's calls for a cease-fire in Idlib were bearing fruit after days of relative calm.
"It looks like we obtained a result with the efforts which were made," he told reporters on a flight back from Azerbaijan. "But we are still not satisfied."
Turkey has established military observation posts around Idlib, which Ankara has reportedly reinforced with troops and equipment in recent weeks.
Erdogan said these posts are aimed at protecting the "innocent people" there, according to Hurriyet.
"But currently everybody can see the regime's mercilessness and the terror that they are spreading there. There is a terror state," he added.
While backing separate sides, Turkey, Russia, and Iran launched a negotiations process last year in the Kazakh capital, Astana, mainly dealing with battlefield issues, such as cease-fires and deescalation zones. A separate UN-led round of talks addressing political issues has taken place in Geneva.
The United Nations expects up to 900,000 people to flee if Syrian government forces launch a large-scale offensive on Idlib, home to some 3 million people.
The 7 1/2-year war has killed more than 400,000 people and displaced millions.