Russia, Turkey and Iran have failed to hammer out details on an agreement over the war in Syria, including the boundaries and policing of four safe zones previously agreed, according to Moscow's chief negotiator.

Russia’s Alexander Lavrentiev said on Wednesday that documents outlining how the four zones should work "need finalising" despite being "essentially agreed" between the three key powerbrokers, after two days of negotiations in Kazakhstan.

He added that there had been no definitive agreement over the contentious issue of "which specific forces" would police the zones.

However, the three sides have formed a working group to finalise an agreement on creating de-escalation zones in Syria, according to a joint statement.

The countries previously said they would hold the next round of talks in Astana in the final week of August.

Moscow and Tehran, which back Syrian President Bashar al-Assad, and rebel supporter Ankara agreed in May to establish four de-escalation zones in a potential breakthrough towards calming a war that has claimed an estimated 320,000 lives since March 2011.

While fighting dropped off in the weeks after the deal, it has ratcheted up in some areas since, and the international players have yet to finalise the boundaries of the zones or determine who will police them.

Al Jazeera's Andrew Simmons, reporting from Astana, said Russia announced that it would call on the members of the Commonwealth of Independent States (CIS) to deploy protection forces in the de-escalation zones.

“Now that is a development, but it is just a call and it doesn’t prove that there is an agreement over the issue,” he added.

The CIS was formed after the collapse of the Soviet Union in 1991 as an organisation that is a loosely arranged group of countries.

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In an effort to thrash out the details of the plan on Syria, the three sides held a string of closed-door meetings for a second day in Astana on Wednesday, with the participation of representatives of Syrian government and opposition.

Speaking to Al Jazeera from the US state of Virginia Wa'el Alzayat, a former advisor to Samantha Power - the former US ambassador to the UN - said there was no new development coming out of the latest rounds of talks.

"This is really more of the same of what has been tried under the previous administration in terms of dangling the prospect of further cooperation perhaps against ISIL or now to administer areas after ISIL has been defeated in exchange of the need of de-escalation and ultimately a sort of a political resolution." Alzayat said.

"What is not there is the need to have a political transition in Sria... preferably one that includes Asad leaving power." he said.

Syria's conflict evolved from a bloody crackdown on protests in 2011 to a devastating war that has drawn in world powers, including Russia and a US-led international coalition.

Russia has been pushing the talks in Astana since the start of the year as it seeks to pacify Syria after its game-changing intervention on the side of Assad.

The talks have largely seen the West sidelined, but they are intended to complement broader political negotiations the United Nations is backing in Geneva, which are due to restart next week.