Chief regime negotiator Bashar al-Jaafari insisted that discussions were still "in a preparatory phase," only a day after UN special envoy Staffan de Mistura announced the Geneva talks had officially started.
"We are still in the preparatory phase for indirect talks ... We still don't know who the opposition delegation is," Jaafari told reporters after meeting de Mistura.
"We also asked for the names of participants and the agenda of indirect talks... We are waiting to know... Whom we will negotiate with," he said, saying the opposition delegation was not made up of "professional politicians".
He said he expected the talks to be "complicated and difficult" but hoped they would "achieve something" in time for a mooted meeting of key outside players announced by Russia for February 11 in Munich, Germany.
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In another sign that political momentum had slowed, HNC representatives told journalists they would not attend a scheduled meeting with de Mistura today.
"There is no meeting with de Mistura," said HNC member Farah Atassi.
The HNC has demanded the regime allows humanitarian access to besieged towns, stops bombing civilians and releases thousands of prisoners -- some of them children -- languishing in regime jails.
"We are waiting for an answer from de Mistura on what we discussed yesterday. We need to see the lifting of sieges," HNC spokesman Salem al-Meslet told reporters.
Since the conflict began in March 2011, more than 260,000 people have died and more than half of Syria's population have fled their homes.
The chaos has also fuelled the rise of the Islamic State (IS) extremist group which has overrun swathes of Syria and Iraq and staged a raft of deadly attacks across the globe, including in Paris in November.
The extremist Sunni Muslim group claimed responsibility for multiple blasts on Sunday on a revered Shiite shrine south of Damascus that killed at least 70 people.