TEHRAN (Reuters) - A blast in a mosque in Iran that killed at least 12 people was an accident and not an attack, a senior official said on Sunday, but others cautioned the investigation into the cause was continuing.

Iranian media had reported that a bomb exploded in a crowded mosque in the southern city of Shiraz on Saturday evening. About 200 people were wounded and some were in a critical condition.

State television carried footage showing wooden debris and pieces of brick strewn on the mosque’s carpet-covered floor and ambulances and fire engines rushing to the scene.

“Last night’s explosion in Shiraz was as a consequence of an accident and not the planting of a bomb,” the official IRNA news agency quoted the deputy interior minister in charge of national security, Abbas Mohtaj, as saying.

He did not give details, but state Press TV television said the blast may have been “caused by explosives left behind from an earlier exhibition commemorating” the 1980-88 Iran-Iraq war.

The semi-official Fars News Agency carried a similar report.

“The cause of the incident was probably laxness since a defence fair was held at this place some time ago,” it quoted the commander of security forces in the southern Fars province, Ali Moayedi, as saying.

But Foreign Ministry spokesman Mohammad Ali Hosseini said the investigation was continuing, and “therefore no pre-judgement can be made about the incident”.

The deputy head of parliament’s national security commission, Mohammad-Nabi Roudaki, said the possibility of a terrorist attack had not yet been ruled out.

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Security is normally tight in Shi’ite Muslim Iran and bomb attacks have been rare in recent years. But several people were killed in 2005 and 2006 in blasts in a south-western province with a large Sunni Arab population.

Tehran has in the past accused Britain and the United States of trying to destabilise the Islamic Republic by supporting ethnic minority rebels operating in sensitive border areas.

Fars News Agency on Saturday quoted a police official as saying a “hand-made” device had been planted in the mosque.

The governor of Fars province said on Sunday the death toll had risen to 12 from nine initially reported after the blast.

The explosion took place in the male section of Shiraz’s Shohada mosque during an address by a cleric. People in Shiraz, a city of more than one million inhabitants and a popular tourist destination, were urged to donate blood for the wounded.

A man carrying a blood-stained shirt said he and others were knocked unconscious by the force of the blast: “We went to the mosque after the evening prayer ... when suddenly there was the sound of an explosion and then we did not feel anything.”