Russian news agencies reported that a three-way meeting gathering the co-sponsors of the talks, Russia, Iran and Turkey, was underway in the Kazakh capital Astana, aimed at cementing four conflict-free areas agreed in May.
The two days of meetings are then set to involve a string of bilateral talks before a plenary session bringing together all the participants on Wednesday.
Anuar Zhainakov, press-secretary at Kazakhstan's foreign ministry, confirmed to AFP that delegates from the Syrian regime of Bashar al-Assad and the rebel factions that oppose him had also arrived in Astana.
The deal laid out the areas where rebels and government forces should halt hostilities, including air strikes, for six months. More than 2.5 million people are believed to live in the zones.
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Violence decreased markedly across all four areas in the first weeks after the deal was announced, although it ramped up in Daraa.
However, the sides failed to meet a June 4 deadline to determine the exact boundaries of the zones and it remains unclear how and by whom they will be policed.
Of all the four zones, which also take in the northwestern province of Idlib, parts of the central province of Homs and opposition-controlled Eastern Ghouta near Damascus, it is the southern zone that has seen the worst fighting in recent weeks.
While Damascus has spoken in support of the zones deal, the rebels have been far more pessimistic and slammed any Iranian involvement in the plan.
Syria's conflict evolved from a bloody crackdown on protests in 2011 to a devastating war that has drawn in world powers, including Russia and a US-led international coalition.
Russian has pushed the talks in Astana since the start of the year as it seeks to pacify Syria after it game-changing military intervention on the side of Assad.
The talks in Astana complement broader political negotiations the United Nations is backing in Geneva that are due to restart in mid-July.