The blast went off just after a prayer sermon by prominent local cleric Mohammad Anjavinejad, who is known as a vehement critic of Wahhabism -- the ultra-conservative form of Sunni Islam practised in Saudi Arabia.

Writing at the Jerusalem Post last November, Iran analysts Meir Javedanfar and Alex Vatanka, contributors to Jane's defense oriented publications, describe the 2007 assasination of another Iranian cleric, Hojjatoleslam Hesham Seimori, known for his anti-Saudi and anti-Wahhabi views, ostensibly by Iranian-based Sunnis connected to al Qaida:

Three days later, as Seimori's family and friends gathered in his mosque to mourn his passing, they found CDs scattered around the building. The CDs contained a stark warning from al-Qaida stating that Iran should stop its support of Iraq's Shi'ites, and that it would otherwise be considered as a legitimate target for Sunni jihadists. This message was repeated in an audio tape released on July 9, where Abu Omar al-Baghdadi, a purported leader of the al-Qaida-affiliated Islamic State of Iraq, gave Teheran an ultimatum until September 9 to walk away from Iraq and cease its support for Shi'ite parties or expect "fierce war" which would strike "every spot" where Iranians are found.

IRANIAN officials and media scantly noted the al-Qaida ultimatum, and most of the related reporting was by Farsi-language outlets based outside Iran. Teheran's silence can be explained by its desire to avoid panic among its public, given fears that the carnage in Iraq has the potential to spill over into Iran. The alternative view is that Teheran considers al-Qaida's threats mere bravado and untenable as the latter find itself growingly isolated among Iraq's myriad of militant groups.

The suggestion that Iran may be experiencing a form of blowback by Al Qaida-linked Iranian Sunnis for its alleged support to Shiite militants in Iraq is needless to say an interesting one. As in Iraq's Saddam Hussein and Afghanistan's former Taliban rulers, it's not the first time that the US and Iran have found themselves sharing strategic enemies. Even as Washington accuses Iran of surpassing Al Qaida as the chief threat to Iraq, and of stepping up its support to Islamist militant groups in the region across the Sunni-Shiite divide, including notably the Sunni Islamist Palestinian group Hamas.

Washington-based Iran analyst Trita Parsi, an advocate for greater US engagement with Iran, tends to doubt the official Iranian line that the Shiraz mosque explosion was an accident caused by the storage of ammunition in the mosque dating back to the Iran-Iraq war. "Could be though Tehran definitely has an incentive to give the impression that all is under control and that such things cannot happen in Iran," Parsi writes me. "The timing of the explosion makes it suspect..."

"Al Qaida has actually been targeting Iran quite a lot, but it’s received very little media attention in the West," Parsi adds.

And there could be more Al Qaida problems for Iran in coming months and years, Javedanfar and Vatanka suggest, as an outgrowth of the US reducing its presence in Iraq. "An undefeated and still vehemently anti-Shi'ite al-Qaida could then redirect its efforts against the largest and most powerful Shi'ite state in the world, Iran."