"Investigations by relevant bodies have accurately determined the cause of the accident at... Natanz nuclear complex," said a spokesman for Iran's Supreme National Security Council, referring to one of the country's main uranium enrichment plants.

"Due to certain security concerns the cause and details of this accident will be announced at the proper time," state news agency IRNA quoted Keyvan Khosravi as saying.

The Islamic republic's nuclear body said the incident happened Thursday at a warehouse under construction at the complex in central Iran, saying it caused no casualties or radioactive pollution.

Iran's Atomic Energy Organization gave no further details, but Natanz governor Ramezan-Ali Ferdowsi told the Tasnim news agency that a fire had broken out at the site.

Hours after the announcement on Thursday, IRNA published an editorial warning Iran's arch-foes against hostile actions, saying that unnamed Israeli social media accounts had claimed the Jewish state was behind the incident.

"If there are signs of hostile countries crossing Iran's red lines in any way, especially the Zionist Regime (Israel) and the United States, Iran's strategy to confront the new situation must be fundamentally reconsidered," the agency said.

Iran's nuclear body has yet to provide an explanation for the cause of the incident, which came six days after an explosion near a military complex in Parchin area southeast of Tehran rocked the Iranian capital.

Authorities blamed that blast on "leaking gas tanks".

Parchin is suspected of having hosted conventional explosion tests with nuclear applications, which the Islamic republic denies.

Tehran announced in May last year it would progressively suspend certain commitments under a 2015 nuclear deal with major powers, unilaterally abandoned by the United States in 2018 followed by the reimposition of biting sanctions.

Iran restarted enriching uranium at Natanz last September after having agreed under the accord to put such activities there on hold.

Tehran has always denied its nuclear programme has any military dimension.