Staffan de Mistura says many civilians dead in air strikes on Zabadani causing “unprecedented levels of destruction”.
A 48-hour ceasefire is under way in the Syrian town of Zabadani and two villages in the northwestern province of Idlib after an agreement was struck between pro-government forces and rebel groups.
The truce started at 6am local time (3.00GMT) in the rebel-held town of Zabadani north of Damascus as well as two Shia villages, Al Foua and Kafraya.
According to the UK-based Syrian Observatory for Human Rights, the ceasefire was agreed upon between the Lebanese-based group Hezbollah, which is supporting the Syrian government, and the Nusra Front-aligned group, Ahrar al-Sham.
A Hezbollah spokesperson told Al Jazeera that negotiations on a ceasefire had been taking place for the past 10 days and the UN’s special envoy for Syria, Staffan de Mistura, was involved.
The observatory said the ceasefire would allow buses to carry the Ahrar al-Sham fighters to retreat from Zabadani and aid to be delivered to civilians in all of the towns.