Syrian activists have threatened a "volcano of rage" over the Houla killings of civilians while state media called for nationwide prayers in memory of the victims.

On the first Friday since the killings, activists called on Syrians to rise up across the country in honour of the 49 children who were among the 108 dead counted by the UN mission.

"A new volcano of rage is exploding thanks to them," protest organisers said on their Syrian Revolution 2011 Facebook page. "For those pure souls who sacrificed themselves at the altar of our freedom and sacrificed their blood... tomorrow Friday, we will rise up in such a resounding way, and we promise them, there will be no second Houla."