"To this moment, all delegations, which participate in the Astana process, have arrived in the Kazakh capital, including the representatives of the Syrian armed opposition," Zhainakov told reporters, according to Sputnik on Tuesday.
He added that the delegations will hold negotiations in the bilateral format on Tuesday, while on Wednesday a plenary session will take place.
The fifth round of the talks, which are aimed at securing a lasting ceasefire in the war-ravaged Arab country, will conclude on Wednesday.
Iran and Russia, along with Turkey, a backer of the Syrian government’s armed opponents, signed a deal to establish the zones in Syria in the previous round of talks early May.
The three countries, which are guarantors of an ongoing ceasefire covering most of Syria, held consultations in Astana on Monday, a day before the meeting begins.