The deal was reached along with Jordan, according to U.S, Secretary of State Rex Tillerson who spoke at a news briefing at the summit and the agreement covers an important area in Syria that affects Jordan's security and a very complicated part of the Syrian battlefield.

"This de-escalation area was agreed. It's well-defined -- agreements on who will secure this area. A cease-fire has been entered into. And I think this is our first indication of the U.S. and Russia being able to work together in Syria," Tillerson said.

Areas in which acts of aggression are nominally prohibited would cover Idlib and certain parts of the Latakia, Homs, Aleppo and Hama provinces, along with Damascus, Eastern Ghouta, Daraa and Quneitra, according to the deal. 

In separate talks in the Kazakh capital of Astana in May, Turkey agreed with Russia and Iran on a plan to establish a network of “de-escalation zones” in different regions of war-torn Syria.

The American diplomatic is optimistic about the success of the deal because it is different compared to similar cease-fire deals in Syria between the U.S. and Russia in terms of the level of commitment on the part of the Moscow, he said. 

"Russia has the same, I think, interest that we do in having Syria become a stable place, a unified place, but ultimately a place where we can facilitate a political discussion about their future, including the future leadership of Syria," Tillerson said, adding that the Trump administration sees no long-term role for the Syrian President Bashar al-Assad’s family or his regime.

How Assad "leaves is yet to be determined”, he said but emphasized there would be a transition away from the Assad government.

"We have certainly made it clear in our discussions with Russia, that we do not think Syria can achieve international recognition in the future," Tillerson said. "Even if they work through a successful political process, the international community simply is not going to accept a Syria led by the Assad regime."

Syria has been locked in a vicious civil war since early 2011, when the government cracked down on pro-democracy protests. 

More than 250,000 victims have been since killed and in excess of 10 million displaced, according to the UN.

Anadolu Agency