Snipers opened fire on Wednesday as hundreds of protesters surrounded two vehicles carrying United Nations monitors, as they drove through the town of Arbeen, on the outskirts of Damascus.
More than half a dozen observers are in the country, with more set to arrive, to begin monitoring a fragile ceasefire that many commentators say appears to be holding in most of the country.
Amateur video uploaded on Wednesday purportedly showed activists shouting for Syrian rebels to be armed by the international community, when suddenly at least one gunshot rang out.
The shot caused panic among the demonstrators sending them running for cover. Activists claim several further shots were fired and that eight protesters were injured.
The video could give an indication of the difficulty facing UN teams as they seek to monitor whether government forces and Syrian rebels are keeping to a seven day old truce.
Activists reported continuing shelling in suburbs of Homs while the state news agency reported a bomb attack in Idlib province on Wednesday.