On Saturday night in Tehran, members of a pro-government militia broke into a mosque where former President Mohammad Khatami, a reformist leader, was speaking, forcing him to break off before concluding his remarks. “about 50 vigilantes armed with chains, batons and pepper spray disrupted a speech by Mr. Khatami at Jamaran Mosque in Tehran, the home mosque of Ayatollah Ruhollah Khomeini, the spiritual leader of Iran’s Islamic Revolution.” Citing a report on the event by an Iranian news source, the American Web site Tehran Bureau said that the disruption came after Mr. Khatami had seemed to draw an explicit parallel between the opposition movement and the struggle of Imam Hussein, the revered Shiite martyr whose death is being commemorated this weekend. According to the report, Mr. Khatami said, “Imam Hossein’s rebellion arose from his willingness to die for the sake of freedom. He fought against those who wanted to govern society in the name of religion and abolish freedom.”