Sunday’s explosion occurred at a steel plant in the city of Yazd, killing seven people and seriously wounding 12 others. Several of the victims were foreigners, according to Iranian officials.
Officials initially attributed the blast to water accidentally coming into contact with heated implements.
Later, a local member of parliament, Ali Akbar Oliaw, said the blast had been touched off by defective ammunition that had been included in the scrap metal brought to the privately owned plant.
Iran has not identified the type of steel being manufactured at the plant.
Citing Western intelligence sources, the German newspaper Die Welt reported last month that North Korea has been providing Iran and Syria with maraging steel, which can be used in centrifuges that enrich uranium.
The steel’s strength and malleability also make it useful in construction of exhaust systems for missile engines. The U.S. and other countries monitor the import and export of maraging steel because of its possible use in centrifuges.
The steel plant explosion follows two similarly mysterious blasts at sensitive Iranian sites in November - one at a missile base that killed a key figure in the Islamic republic’s missile program and another at a suspected nuclear weapons facility.
In all, there have been four unexplained explosions at key Iranian sites since October 2010. In addition, a scientist working in Iran’s nuclear program was killed in Tehran in July.
Israeli military analyst Ron Ben-Ishai wrote in Sunday’s Yediot Achronot newspaper that the steel plant explosion might have been a simple accident, but in view of the other recent explosions “it is hard to reject the possibility that this was intentional sabotage.”
He noted that Sunday’s blast had come at a time not usually considered a work hour and that the mention of foreigners among the dead could be a reference to North Korean experts who had come to train Iranians in processing the steel.
Western nations have accused Iran of trying to create an atomic weapon, but Tehran has said its nuclear program has only peaceful aims.