"Jabhat al-Nusra today fired rockets into the neighborhoods of Mashariq, Ashrafiya, Zahra and Sheikh Maqsoud — places where Kurds live. The streets of the Bani Zaid block have been attacked by snipers for several hours," the source told RIA Novosti.
The group also reportedly attacked a number of Syrian army and people's militia checkpoints in Aleppo, the source said.
"The number of terrorists was small, the fight was short-lived and the militants retreated," the source added.
The attacks have resulted in no casualties, according to the source.
Russia and the United States reached an agreement on a ceasefire in Syria on February 22. The ceasefire took effect at midnight on Saturday, Damascus time (22:00 GMT on Friday).
The cessation of hostilities does not apply to terrorist groups operating in Syria, such as the Nusra Front, which is banned in Russia.
A source told RIA Novosti on Saturday that militant groups allied with the Nusra Front opened fire in civilian areas of Aleppo and Homs after midnight.