All three countries are sponsors of the latest round of ceasefire talks underway in Astana, Kazakhstan, and a largely ignored ceasefire that was signed late last year. Russia and Iran are both key backers of Syrian President Bashar al-Assad, while Turkey supports Syrian opposition forces.
The preliminary agreement, signed in Astana, was put forward by Russia and would create security zones in Idlib province, to the north of the city of Homs, in Eastern Ghouta near Damascus, and in the south of Syria, Russian state-run Sputnik news agency reported.
A working group will later decide "boundaries of disarmament, areas of tension and security areas, as well as to address technical issues related to the implementation of the memorandum," Sputnik said, citing the signed document. The Russian agency said maps demarcating the areas in question would be completed by May 22.
Such zones -- also referred to as non-conflict or safe zones -- are meant to be areas where civilians can live without being targeted by any party in Syria's war. However, key issues would involve whether and how the zones would be enforced.
Syria's Foreign Ministry said Wednesday it accepted the Russian proposal to create de-escalation zones, vowing not to shell these areas in compliance with the December ceasefire agreement.
But Osama Abu Zeid, a member of the opposition High Negotiations Committee, told reporters Thursday in Astana that the Syrian armed opposition rejected any agreement that would divide the country.
Ceasefire violations claimed
Abu Zeid also insisted any ceasefire agreement should apply to the entire Syrian territory, saying the Hama area remains under attack by regime forces.
The armed opposition suspended its participation in the peace talks Wednesday, citing continued regime violations of the ceasefire agreement signed in December. The opposition groups staged a walkout during Thursday's discussion in objection to the agreement, Reuters and Agence France-Presse reported.
Abu Zeid said Russia had failed as a guarantor of the ceasefire agreement. "Russia doesn't want to and can't keep its vows," he told reporters.
"We are taking part in negotiations, not to make concessions, but to achieve what we've tried to achieve with arms. If we can't, we will go back to armament."
The Syrian Foreign Ministry said regime forces would continue fighting terrorists from ISIS and al Qaeda's former affiliate in Syria, al Nusra Front, according to a statement carried by the state-run Syrian Arab News Agency.
Opposition claims ceasefire violations
Russian President Vladimir Putin, speaking after a meeting Wednesday in Russia with his Turkish counterpart, Recep Tayyip Erdogan, said he was in favor of creating de-escalation zones in Syria to "cement" the ceasefire
in the country.
Putin and US President Donald Trump also discussed the idea of de-escalation zones in a phone call
Tuesday. The Trump administration, which has sent a representative to the Astana talks, has not spelled out in detail how its own plan for safe zones would work.
Alexander Lavrentyev, the Russian presidential envoy to the Astana talks, said Thursday that his country will continue to work with the United States "to find the most effective mechanisms of interaction on the Syrian soil," Russian state news agency Tass reported.
Lavrentyev said Russia would do all it could to ensure Syrian warplanes no longer operate over the de-escalation zones, according to Tass.
"Russia is ready to take part by sending its observers to the so-called safety line zones to participate in monitoring compliance with the ceasefire and to fix violations," he reportedly said.
Turkey's Foreign Ministry said it welcomed an agreement that would stop the use of weapons and help bring urgently needed humanitarian relief to Syria.
UN urges progress
Staffan de Mistura, the UN special envoy for Syria, told reporters Wednesday he was "very concerned at the reports of escalation in Syria, including, allegedly, reports of (airstrikes), particularly in this delicate moment in the Astana discussions where actually proposals to de-escalate the conflict are under very serious discussion."
He urged all sides to press ahead with efforts to halt the fighting and build confidence.
"Every time we have been having a meeting or a discussion about cessation of hostilities, or de-escalation in this case, there have been some incidents produced by one side or the other," he said. "The secret is to try to make sure that those incidents stop but also do not kill the opportunity for good news related to that."