The UN expert delegation is led by Milos Strugar.
The Delegations from Damascus, Turkey and Iran had already arrived in Astana for the talks. Representatives of the Syrian armed opposition, mainly from the South Front, may come later on Tuesday.
The first round of Astana talks on Syria brokered by Russia, Turkey and Iran were held on January 23-24 and resulted in a Moscow-Tehran-Ankara agreement on the establishment of a trilateral mechanism to monitor the ceasefire in Syria.
The second round of the Astana talks took place on February 15-16, with the participants agreeing to set up a ceasefire monitoring group, encompassing Iran, Russia and Turkey, that would report to the United Nations.