The 'Free Syrian Army' sprays graffiti on two UN observer vehicles and places a green-white-black flag on its back. While they intimidate the observers they chant that the observers are afraid of passing through Duma. When one of the observers gets out to remove the inappropriate flag they almost ambush him.

Many incidents have been reported of observers being ambused with iron rods and shot at. However, propagandist outlets fail to note the taunts and fail to identify the culprits ('Free Syrian Army') through selective reporting. The militias do not want the observer mission in Syria, because its aim is peace and they believe that they must fight on and cause so much death and destruction, and blame it on the government, in order to make an international intervention inevitable.

The militias have been known to even plant IEDs on UN vehicles:

http://www.liveleak.com/view?i=9c6_1337206301 Terrorists Plant Explosive Device On UN Monitors Vehicle And Film It For Propanganda As A Government Missile Attack- May 15th 2012