Not sure if this is the "real" reason, but it's different..

this article describes the factors that affect Russian and Chinese relations with Syria, emphasizing the Iranian dimension of their relationship.

the US is pushing for a legally binding UN Security Council resolution that would make all countries take action to prevent the flow of citizens into terrorists groups, like ISIS. action may include evoking people's citizenship or passport suspect of terroristic activities or aiding terrorists, but before any crime is committed.