Read: Iran deal can speed solutions in Syria, Yemen: Rouhani
The truce between the Syrian army and the Lebanese group Hezbollah on the one side, and Syrian insurgents on the other, came into effect in the town of Zabadani and the Shi'ite Muslim villages of Kefraya and al-Foua on Thursday.
Read: At least 70 dead in Syria regime raids near Damascus: monitor
It had been extended late on Friday but broke down by the morning, said Rami Abdulrahman, who runs the Britain-based Observatory.
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