It did so before, an Iranian blogger reminds us:

Imam Rezais the eighth Imam in Shia Islam and his shrine is located in Mashhad, the capital city of Khorasan, a province in northern east Iran. On June, 1994, a massive blast destroyed portions of the shrine, killing twenty six people (unfortunately, I can't find any picture of the event). The explosion happened in the Ashura decade, the time in each year Shias mourn for Imam Hossein's martyrdom .

People's Mujahedin of Iran (PMOI), a terrorist Iranian organization based in Iraq at the time, accepted the responsibility. The guy assumed to be responsible for the blast was killed in a shooting.

However, after Saeed Emmami, a high ranking official in Iranian Intelligence, was arrested and charged with assassinating opposition figures, he also confessed that his group had links to the the bombers. This event, like many others in recent Iran's history, was never fully investigated and clarified.

There is little doubt that inflaming Iraq is in Iranian interest and there is no doubt but that this suicide bombing was intended to do just that. So, inquiring minds wonder.