Kazakh Foreign Ministry spokesman Onuar Zhainakov said that the talks had been extended and some rebel groups had agreed to take part.
"We expect the arrival of representatives from the northern and southern fronts of the armed Syrian opposition," Zhainakov said, according to AP.
However, two rebel officials immediately dismissed the report.
Mamoun Haj Mousa, from the Suqour al-Sham Brigade, said there are no plans for factions to attend the talks and another opposition official, Yahya al-Aridi, simply stated, "Let them say what they wish."
The Astana talks, brokered by Russia and Turkey, are centered on reaching a ceasefire in Syria and getting humanitarian relief to millions of suffering civilians. They run parallel to the UN-mediated political talks in Geneva aimed at ending Syria's civil war.
Rebels announced earlier this week they would not attend the Astana talks because of repeated cease-fire violations by the government.
A government delegation led by Syria's UN ambassador, Bashar al-Jaafari, began meetings Tuesday with Russian officials in Astana.