Ladies and gentlemen, this news is unconfirmed/unverified and has been posted on the web before. As Bharwana pointed out, the territory this shrine is located in is not under the control of Iranian sponsored militias, rather it is under rebel control
At this point, given the war in Syria and the involvement of so many different competing groups and the related propaganda by each group against the other, there is no way to establish the veracity of any of the claims made or which side is responsible.
Since this issue is getting more and more visibility and is taking on sectarian tones, I am re-opening the thread for discussion & clarification.
At this point, I am adding the clarification that the shrine is actually in (non-Shia) rebel controlled territory to the OP. If anyone has information that argues differently, please let the mods know and we will update accordingly.