The blast, early on Tuesday, was caused by the "careless" handling of oxygen canisters at the Sepahan Boresh in Baghershahr, the governor of Tehran's Kahrizak district told IRNA.

The explosion is the most recent in a series of unusual incidents at factories and sensitive nuclear and military sites in recent weeks.

A blast at a medical clinic in Tehran on Tuesday last week killed 19 people. Just two days later, a fire broke out at a nuclear site in Natanz, causing significant damage and harming Iran's capabilities in uranium enrichment. 

Similar incidents have also taken place at power plants, a petrochemical centre, and a military complex believed to house missile production facilities.

Such occurrences have prompted speculation that the Islamic Republic is under attack, perhaps from a foreign power.

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Last week's explosion at the Natanz nuclear plant has in particular been linked to Iran's arch-foe Israel, which has vowed to stop Tehran from gaining nuclear capabilities.

Israel has also been linked to dozens of strikes on Iran-backed militants in Syria, although it rarely confirms or denies such attacks.

On Sunday, Defence Minister Benny Gantz played down speculation Israel was behind the damage to the nuclear site.

"Not every incident that transpires in Iran necessarily has something to do with us," he told reporters.

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