TEHRAN --Iran said on Wednesday that a blast in a mosque that killed 13 people in the southern city of Shiraz last month was indeed a bombing and that the suspected mastermind had been arrested.

"Through the efforts of the law enforcement forces... the main person involved in the Shiraz mosque explosion was arrested in one of the northern cities of the country," the Fars news agency quoted Intelligence Minister Gholam Hossein Mohseni Ejeie as saying.

"The main agent, who was directly an accomplice in the bombing, was arrested during an attempt to leave the country. The person was armed when arrested," Mohseni Ejeie said.

After initial reports that the April 12 explosion, which also wounded more than 200, was the result of a bombing, officials had insisted that it was accidental.

An interior ministry body said the blast was set off by munitions on display in the mosque as part of an exhibition commemorating Iran's 1980-1988 war with Iraq.

The blast ripped through a packed mosque during an evening prayer sermon by a prominent local cleric.