The regime in Tehran has gone on the defensive following deadly riots on Sunday. By breaking the traditional ceasefire on religious holidays, the regime has angered many conservatives. The government in Tehran could be facing louder and more self-assured demonstrators in the coming days who see their opportunity to force regime change.

Well-equipped policemen beating unarmed demonstrators. That was the image that became synonymous with opposition protests in Iran following the disputed presidential election in June.

But on Sunday the pattern changed. On the holy festival of Ashura, the day on which Shia Muslims commemorate the violent death of their religious leader Imam Hussein, the tide may have turned in Iran.

The pictures and amateur videos coming out of Iran via...