Talks are likely to focus on bolstering a shaky ceasefire on the ground after Moscow, Tehran and Ankara agreed to establish a "mechanism" aimed at ensuring the truce.
Salim al-Muslit, spokesman of the High Negotiations Committee (HNC), also told Reuters the opposition was sticking to its position that President Bashar al-Assad can have no role in the transition, saying "the heavy price paid by the Syrian people" would have been wasted if he remained in power.
The Kazakh Foreign Ministry on Wednesday had confirmed that the beginning of the second round of Astana talks on Syria has been delayed until Thursday noon (06:00 GMT). On Monday, Russian Foreign Minister Sergei Lavrov said he welcomed closer engagement with Washington to fight "absolute evil" in Syria, according to Russian state news agency TASS.
"The government is ready.as part of efforts towards the next meeting in Astana to exchange detainees for men, women and children - civilians and soldiers - kidnapped by terrorists", SANA said, referring to the rebels. Syrian opposition representatives, who have threatened this week to boycott the talks, are not happy with the attitude of Russian Federation to push the regime to comply fully with the cease-fire, a Turkish official told Hürriyet Daily News.
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Muslit, however, said the opposition had yet to receive an agenda for the upcoming negotiations.
United Nations envoy on Syria Staffan de Mistura said he would not participate personally in the latest Astana meeting but that his office would be represented by a "technical team".
A Syrian rebel source has denied that opposition groups have received an invitation to attend peace talks being held next week.