CNN  — 

More than 100 Syrian rebel fighters are being allowed to safely leave a besieged town outside Damascus as part of a U.N.-supported deal.

The Sunni fighters are being given safe passage out of Zabadani, near the border with Lebanon, in exchange for hundreds of Shiite residents being able to exit two besieged towns in northern Syria.

The swap Monday is part of a deal agreed in September amid the complex, bloody civil war that has torn Syria apart.

The agreement, facilitated by U.N. Special Envoy for Syria Staffan de Mistura, included a localized ceasefire aimed at enabling access for humanitarian groups to the besieged areas.

But with distrust heavy on all sides in the conflict, implementing all aspects of the deal has proved tricky. The exchange of fighters and residents from the different towns was supposed to take place last week, but it was postponed at the last minute.

The Sunni rebels in Zabadani had been under siege from Syrian government forces and the Lebanese Shiite militant group Hezbollah. Rebel forces, meanwhile, had surrounded the towns of Kefraya and Fouaa in the north.

The evacuations were taking place Monday, according to the Syrian Observatory for Human Rights, an activist group that monitors the conflict, and Al-Manar TV, a Hezbollah-affiliated station.

Under the deal, the Sunni rebels will end up in Turkey, and the Shiite residents will travel to Lebanon.