The talks holding in the Kazakh capital, Astana, are as a result of efforts by Russia and Iran on one hand as well as Turkey.
Russia and Iran are providing support for the Syrian regime while Turkey supports the rebels fighting the government.
The latest move marks the first time the opposition groups are being represented by a delegation of exclusively armed groups.
The rebels have ruled out engaging in direct negotiations with the government, while the oganisers have played down expectations of a breakthrough.
The last attempt at engaging the Syrian opposition and the government, in talks mediated by the United Nations, was suspended early last year.
