"Terrorist groups shelled Abu al-Duhur humanitarian corridor and the civilians who were crossing it. This is not surprising, because these are their ordinary tactics and they have done this before, when, for instance, humanitarian corridors were organized for withdrawals from al-Wafideen camp in Eastern Ghouta," the source said.
The source added that earlier in the day, the Syrian army had repelled militant attack 21 miles to the north of the city of Hama, located on the border of Idlib province, and killed several militants.
The Idlib de-escalation zone is one of the remaining posts of insurgency in Syria.
Russia, alongside Iran and Turkey, is the guarantor of the Syrian truce regime.
The province of Idlib is the remaining hotspot of militant insurgency in Syria, with the remainder of the country under the regained control of government forces.