"The representatives of the Syrian armed opposition also participate in the negotiations, in meetings. They are already here," Zhainakov told reporters.
He added that the meetings are attended by "representatives of the Syrian armed position, including the Northern and Southern Fronts."
In addition, Zhainakov stressed that it is expected that all delegations would take part in the plenary session scheduled for 10:00 GMT on Wednesday.
"It is expected that all parties to the talks will participate [in the plenary session] … What [agreements] will be adopted at the session is now under discussion at bilateral meetings," Zhainakov said.
Zhainakov also gave an affirmative answer to the question whether the observer states would attend the plenary meeting.
"Ahmed Berry is leading the delegation," Usman said, confirming their participation in today's negotiations.
Jaysh al-Islam leader Mohammed Alloush, who led the delegation of the armed opposition at previous rounds of Astana talks, did not arrive for the fifth international meeting in the Kazakh capital.
The plenary session in Astana is expected to begin at 10:00 GMT on Wednesday.
The fifth international meeting on Syria in Astana takes place on July 4-5, and brings together the delegations from the three guarantor states — Russia, Iran and Turkey — as well as the Syrian sides and the United Nations teams. Jordan and the United States act as observers.
Defining the exact borders of the four deescalation zones in Syria and the monitoring procedures are the main issues on the agenda.