In Aleppo, 25 civilians, including four children, were killed and 120 others wounded after the Takfiri militants shelled the city on Friday, the so-called Syrian Observatory for Human Rights said, The Daily Star reported.
Syria's military declared a unilateral, three-day cease-fire for the entire country on Wednesday.
The announcement came at the start of the Muslim holiday of Eid al-Fitr that marks the end of the holy month of Ramadan.
It was the first truce since a US-Russia-brokered "cessation of hostilities" came into effect on Feb. 27.
Aleppo has been divided between the government forces and militants since 2012, a year after the conflict broke out in the Arab country.
Syria has been gripped by foreign-backed militancy since March 2011. UN Special Envoy for Syria Staffan de Mistura estimates that over 400,000 people have been killed in the conflict, which has furthermore displaced over half of Syria’s pre-war population of about 23 million.