De Mistura plans to launch substantive peace talks on Monday, and said they will focus on the core issues of governance, elections within 18 months and a new constitution.
The round of talks would not run beyond March 24, when there would be a break before resuming, Reuters reported on Wednesday.
The first and previous round of talks convened by de Mistura collapsed within days in early February as Russia was accused of staging an offensive near the Aleppo, Syria's largest city.
The cease-fire has been shepherded by Russia and the United States through the International Syria Support Group, a group of world and regional powers and organizations that includes several Western powers as well as Turkey, Iran and Saudi Arabia.