The UN, US, Iran and host Kazakhstan are also attending the Russia-Turkey brokered talks in the Kazakh capital between the Syrian regime and opposition groups.
Delegates from the Syrian regime and opposition groups were together in the conference hall on Monday at the opening of the peace talks aimed at ending six years of conflict in Syria. But a rebel spokesman said no face-to-face talks with the regime were currently planned.
The Astana meeting was brokered by Turkey and Russia. UN Special Envoy for Syria Staffan de Mistura is also attending, as is the US ambassador to Kazakhstan and an Iranian delegation.
The Syrian regime and the opposition said the focus of the meeting would be strengthening a ceasefire that went into effect in December, but which both sides have accused the other of violating.
The opposition said it was not seeking a political solution to the conflict at the talks.
"We will not enter into any political discussions and everything revolves over abiding by the ceasefire and the humanitarian dimension of easing the suffering of Syrians under siege and release of detainees and delivery of aid," said opposition spokesman Yahya al Aridi.
The head of the Russian delegation, Alexander Lavrentyev, said it was unclear if the regime and opposition would meet face-to-face during the talks, scheduled to run until at least Tuesday.
The Astana meetings follow the announcement of a ceasefire in Syria last month. Turkey and Russia brokered the ceasefire and set up the peace talks.
The talks do not include every group fighting in Syria. Among those excluded are Daesh and the PYD, which Turkey considers the Syrian arm of the PKK, labelled a terrorist group by Turkey, the EU and the US.
TRT World 's Hasan Abdullah in Astana has more on what is expected at the talks.
Ongoing struggle in Syria
Turkish fighter jets continued over the weekend to hit Daesh targets in northern Syria. Turkey is backing rebel forces attempting to dislodge Daesh from the town of al Bab.
Turkey's military said it killed sixty-five Daesh members on Sunday as part of its Operation Euphrates Shield, designed to protect Turkey's borders.
Russia on Monday also said its forces had targeted Daesh.
Six TU-22 strategic bombers carried out air strikes near the eastern Syrian city of Deir al-Zor on Monday, Russian news agencies reported, citing the defence ministry.