Tehran's statements about this explosion have become increasingly curious. It occurred at a mosque associated with a Shiite cleric who is especially critical of Sunni extremism.

Just afterward, several sources – including the Shiite cleric – claimed that the explosion was the result of a bombing by a radical Sunni group affiliated with al-Qaida.

The Shiite-dominated Iranian government, though, denied these stories, claiming at first that the explosion was not a bombing, but the result of an accident.

More recently, however, Tehran has stated that the Shiraz explosion was a bombing after all, and that the perpetrators were monarchists who received support from America, Britain, and Israel.

All this is very odd. How could Tehran have mistaken a bombing for an accident? And why would America, Britain, and Israel want to bomb the mosque of a Shiite cleric who preaches against Sunni radicalism, which these three governments also oppose? If they were going to bomb anything inside Iran, surely they would seek to destroy targets of far more concern to them, such as Iran's nuclear facilities.

Tehran's first claiming that the Shiraz explosion was not a bombing and then that it was one perpetrated by the West raises the possibility that what it really wants is to suppress the story about the bombing being the work of al-Qaida affiliates inside Iran.

For to admit that this story is true, or even accept the possibility that it might be, would be very difficult and painful for Tehran to do.

Doing so would be an acknowledgment that despite all Tehran's anti-American and anti-Israeli actions and rhetoric, al-Qaida and other Sunni radicals do not accept Shiite Iran as an ally, but instead see it as an enemy – just like America or Israel.

What this would mean, of course, is that even the Islamic Republic of Iran has reason to fear al-Qaida and its affiliates. This being the case, it would be better off making common cause with the United States and other governments opposed to al-Qaida.

But for Tehran to even consider this possibility would call into serious question the wisdom of continuing Iran's anti-American foreign policy.

And this is something Tehran does not want to do since up to now, much of its justification for keeping strict limits on democracy has been based on its claim that this is necessary in order to resist U.S. "interference" in Iran's internal affairs.

If, however, radical Sunni attacks inside Iran are occurring, Tehran will sooner or later have to respond with more than statements about how these are accidents or the work of America, Britain, and Israel.

Tehran may even have to reassess whether America or al-Qaida is more of a threat to it.

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Mark N. Katz is a professor of government and politics at George Mason University.