There was no immediate claim of responsibility for the attack, which came amid tension with the West over Tehran's nuclear work and supply of arms for Russia's war in Ukraine, as well as months of anti-government demonstrations at home.
The extent of the damage could not be independently confirmed. Iran's Defence Ministry said the explosion caused only minor damage and no casualties.
Iranian media video showed a flash of light at the plant, which the official IRNA news agency described as an ammunitions factory. Footage showed emergency vehicles and fire trucks outside the complex.
"Around 2000 GMT on Saturday night, an unsuccessful attack was carried out using micro Aerial Vehicles (MAVs) on one of the ministry's workshop sites," the Defence Ministry said in a statement carried by Iran's state TV.
It said one drone was shot down and the other two were caught in defence traps and blown up. It caused only minor damage to the roof of a workshop building. There were no casualties."
The attack has not affected our installations and mission...and such blind measures will not have an impact on the continuation of the country's progress.
Separately, IRNA reported early on Sunday a massive fire at a motor oil factory in an industrial zone near the northwestern city of Tabriz. It gave no information about the cause of that blaze.
Iran has in the past accused its arch enemy Israel of planning attacks using agents inside Iranian territory. In July 2022, Tehran said it had arrested a sabotage team made up of Kurdish militants working for Israel who planned to blow up a sensitive defence industry centre in Isfahan.
An Israeli military spokesperson declined comment when asked if Israel had a connection to the latest incident. Israel has long said it could attack Iran if diplomacy fails to curb Tehran's nuclear or missile programs, but has a policy of withholding comment on specific incidents.
Several Iranian nuclear sites are located in Isfahan province, including Natanz, centre piece of Iran’s uranium enrichment program, which Iran accuses Israel of sabotaging in 2021. There have been a number of explosions and fires around Iranian military, nuclear and industrial facilities in recent years.
Talks between Tehran and world powers to revive a 2015 nuclear pact have stalled since September 2022. Under the pact, abandoned by Washington under President Donald Trump, Iran agreed to limit nuclear work in return for easing of sanctions.
Iran has acknowledged sending drones to Russia but says they were sent before Moscow's invasion of Ukraine last year. Moscow denies its forces use Iranian drones in Ukraine, although many have been shot down and recovered there.
