"The Syrian army repelled a major al-Nusra Front attack in Qalamoun, there are no dead among the troops. A large number of terrorists have been killed, militant units have retreated," the source said.
Syria has been mired in civil war since 2011, with government forces fighting numerous opposition factions and Islamic extremist groups.
The Russia-US brokered ceasefire regime in Syria came into force on February 27. Al-Nusra Front and Daesh terrorist groups are excluded from the truce.