Iran’s nuclear body said a fire last month at a major nuclear facility in Natanz was caused by sabotage.
But the Iranian Atomic Energy Organization (IAEO) has not said who it believes is behind the incident.
Some Iranian officials have previously said the fire could be the result of cyber sabotage.
It comes after a number of fires and explosions at power plants and other sites in recent weeks.
IAEO spokesperson Behrouz Kamalvandi told state broadcaster al-Alam on Sunday that “the security authorities will in due course reveal the reason [Natanz] explosion ».
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The fire struck a central centrifuge assembly shop. Centrifuges are needed to produce enriched uranium, which can be used to make reactor fuel as well as material for nuclear weapons.
Incident at the Natanz nuclear site
July the 5th
Kamalvandi said last month that Iran would replace the damaged building with more advanced equipment, but the fire could slow the development and production of advanced centrifuges “in the medium term”.
An article by Iranian news agency Irna previously addressed the possibility of sabotage by adversaries such as the United States and Israel, but did not directly blame either country.
Why is Natanz important?
Natanz, about 250 km (150 miles) south of the capital Tehran, is Iran’s largest uranium enrichment facility.
Earlier this month, Bloomberg released details of a report by the International Atomic Energy Agency (IAEA), the UN’s nuclear watchdog, which concluded that Iran was trying to boost the uranium enrichment at the plant.
If true, the move would be in violation of a nuclear deal Iran signed in 2015 with several world powers.
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As part of the deal, Iran agrees to produce only low enriched uranium, which has a 3-4% U-235 concentration and can be used to produce fuel for nuclear power plants. Military grade uranium is 90% or more enriched.
Iran has also agreed to install no more than 5,060 of the oldest and least efficient centrifuges at Natanz until 2026, and not to carry out any enrichment at its other underground facility, Fordo, until 2031.
In return for concessions to its nuclear program, Iran obtained relief from international sanctions.
But last year, Iran began to back down on its commitments after US President Donald Trump abandoned the nuclear deal and reinstated crippling economic sanctions.
In November, Iran said it had doubled the number of advanced centrifuges operated at Natanz and started injecting uranium hexafluoride gas into Fordo’s centrifuges.
Natanz is one of several facilities monitored by the IAEA to ensure Iran’s compliance with the 2015 agreement.
On Saturday, the new IAEA chief Rafael Grossi announced that he would travel to Tehran on Monday to request access to two suspected former nuclear sites. The IAEA said it suspected activities related to the development of nuclear weapons had been carried out in the early 2000s at these sites.
Iran has previously insisted that its nuclear program is not for military use. Officials also denied that Mr Grossi’s visit was linked to steps the United States took at the UN Security Council to reimpose international sanctions on Tehran, state media reported.