Eyewitnesses and some local officials say it appeared to be a bomb blast, while Iranian officials in Tehran say the explosion was accidentally caused by leftover ammunition from an exhibition recently held in the mosque.
The latest official figures say 12 people died and some 200 were injured in the explosion at the Hosseynieh Seyed al-Shohada Mosque in the southern city of Shiraz on April 12.
The explosion happened as the main cleric, Hojatoleslam Mohammad Enjavinejad, was leading his regular service for some 800 people.
A video sent to Radio Farda (see below) of the blast shows worshippers standing in the mosque and listening to religious singing when the explosion goes off and people run and scream in a chaotic scene.
"I was there myself, it was around 9 p.m. when the explosion happened. The [mosque] has separate sections for women and men, the number of victims in the women's section was lower than in the men's section. I even saw some hands that had been blown off," one witness tells Radio Farda.
"It's a bad situation, the number of casualties is worse than the reports on websites, I saw it myself," he adds. "I think that the number of dead and injured is higher...based on what I saw and also because they had mobilized all the ambulances in Shiraz."Distrust Of Official Version
While several officials have said that the blast was accidental, other sources, including Enjavinejad, raised the possibility that the explosion was an attack by unidentified militants.
Some Iranian media initially quoted local officials as saying the explosion was caused by a bomb and suggested that the attack could have been religiously motivated.
But one day later, some officials said the blast was likely caused by ammunition left over from a recent Iran-Iraq War exhibition at the mosque.
On April 13, Foreign Ministry spokesman Mohammad Ali Hosseini said that the investigation was going on and therefore no "prejudgment" should be made about the incident. Iran's judiciary chief, Ayatollah Mahmud Hashemi Shahrudi, has appointed the state inspection organization and the Justice Ministry to head the investigation.
A number of Iranians complained in text messages and phone calls to Radio Farda that Iranian state television did not give much coverage to the story.
Abbas from Kazerun wrote that Iran's state television "is trying very hard to cover up this issue. Please look into it."
Another Radio Farda listener from Iran wrote: "I don't know why none of the officials have sent their condolences [to the victims] of the Shiraz explosion; if a Palestinian child would have been killed then [it would have been different]."
Mashaollah Shamsolvazezin, the spokesman of the Committee To Defend Press Freedom, confirmed in an interview with Radio Farda that Iranian media did not give much coverage to the tragic event.
"The Iranian society has in recent years had a higher level of security than the countries surrounding it. The government and security organs would like to keep this security superiority, therefore any [security breach] is dealt with based on that concept," he says. "The [government's] goals are being realized by restricting the media and not letting them investigate the real cause of the security incidents."
Shamsolvazezin believes that this leads to more people turning to Persian-speaking media outside the country for information on the Shiraz blast and other similar incidents.
Many say the lack of transparency by the government and limited media coverage of the event leads to confusion and conspiracy theories among those Iranians who have little trust in Iranian officials.
Many Iranians told Radio Farda that they doubt the official version of events. They said they believe the casualties are higher than reported and that the explosion was the result of a bomb attack, not an accidental explosion of some leftover explosives.
A number of listeners told Radio Farda they think the Intelligence Ministry or other state bodies might be behind the blast, without giving more explanation.
"The annihilation of the opposition members and creating fear and horror is the New Year's gift [the Iranian New Year began on March 23] of security organs for the innocent people of Shiraz," one caller from Mehrdad said.
Another listener made a similar claim in a message that came from an Iranian number: "This bombing is the work of the establishment's leaders."
Several listeners and some witnesses to the explosion who spoke to Radio Farda also dismissed the official claim that the blast was accidental.
"We went out with my friend for the prayer ablution. I looked at my watch and it was 9:13 p.m. when we heard a terrible sound; it was very scary, there was dust and smoke everywhere," said a woman in Shiraz, who did not want to give her name. "They said a bomb had exploded; the girls had glass in their necks, their faces were bloody, it was horrible."
When asked about the source of the explosion, the woman said she was sure it was a bomb.
Radio Farda asked her: "Why? What did you see to make you think it was a bomb? Officials have said that that there was an exhibition from the war there."
"No, it wasn't from that," she said. "They neutralized the [mines and other munitions] before putting them there."
The reformist "Etemad" newspaper said in an April 14 editorial that the explosion is unprecedented in recent years and it expressed doubt that it was caused by old war munitions.
"Giving reasons such as the explosion of a gas capsule or ammunition from an exhibition -- when such munitions are neutralized and sealed -- show that those who say these things ignore the people's intelligence," the editorial said.Baha'i As Scapegoats
Meanwhile, some observers have expressed concern that the explosion could lead to more pressure on the Baha'i minority in the city.
In recent months, there have been a number of reports about threats and the harassment of Baha'i followers in Shiraz.
Enjavinejad, who is also the head of the Friday Prayers congregation in Fars Province, is known for having preached against Baha'is and Wahhabism. The controversial cleric was quoted on April 14 by the hard-line daily "Kayhan" as saying that it's up to intelligence officials to find out who's behind the explosion. But he added that "we believe that it's possible that Baha'is had a hand in this."
The concern over the fate of Baha'is in Shiraz was also highlighted in several messages by Radio Farda listeners.
"I'm Ahad calling from Shiraz. For now the police forces are trying to portray this as an accident, on the other hand they're pretending they're the victims by showing the injured and dead. It seems that they want to use this in the right moment for their benefit; it means that because of what was being said against our dear Baha'is in the meetings [in the mosque] they want to put the blame on the Baha'is."Radio Farda's Niusha Boghrati contributed to this reportVideo of the Shiraz mosque blast sent to Radio Farda: