A mysterious incident in the early hours of July 2nd badly damaged a building at Iran's Natanz nuclear complex and sparked speculation over the cause.
The incident came at the end of a week marked by two explosions in Tehran, including one near a military site. Officials said the blasts were accidents, but many Iranians suspected covert Israeli operations were responsible.
In a subsequent incident on Tuesday (July 7th), two people died and three were injured when a pre-dawn blast rocked a factory south of Tehran.
Iran's atomic energy agency first reported the July 2nd "accident" had damaged warehouses under construction at the Natanz site, some 250 kilometres south of Tehran, in a confusing statement on the morning after the incident.
There were no casualties, "no nuclear material (on site) and no potential of pollution", agency spokesman Behrouz Kamalvandi told state television.
The organisation released a photo of a damaged building: a long, one-story brick structure with few openings, part of an exterior wall blackened by fire, a collapsed section of roof and doors that appeared to have been blown outwards.
State TV showed images of the building's exterior, but none of the inside.
On Sunday evening, Kamalvandi acknowledged to the IRNA state news agency that the incident had caused "significant financial damage", without elaborating.
But he said the damaged building had been designed to produce "advanced centrifuges", hinting that their assembly had begun prior to the "accident".
Tight security at Natanz
Iran's atomic energy agency on Tuesday denied "false allegations by counter-revolutionary elements in the media of an explosion" at another nuclear plant in Ardakan, around 450 kilometres south-east of Tehran.
"Nothing happened" at the yellow-cake production plant, it said in a statement, adding that rumours are aimed at creating "despair" and supporting the US campaign of maximum pressure against Iran.
The Natanz complex is central to Iran's nuclear programme and is kept under very tight security.
Under the terms of its 2015 nuclear accord with world powers, Tehran had agreed to cap its enrichment of uranium to 3.67%. It also limited the number of so called first-generation enrichment centrifuges to 5,060.
But a year after the US unilaterally abandoned the pact and reimposed crushing sanctions, Iran began progressively stepping away from its commitments.
Since mid-2019, it has enriched uranium to 4.5% -- reactor-grade but still far from the 90% required for military use, and has announced it is working on developing more efficient centrifuges, without limits.
Accident or sabotage?
On Friday, Iran's Supreme National Security Council announced that the "cause of the accident" at Natanz had been "accurately determined".
But it declined to release details, citing security reasons.
On the evening of July 2nd, IRNA published an editorial warning Iran's arch-foes against hostile actions, saying unnamed Israeli social media accounts had claimed Israel was behind the incident.
A Twitter account linked to an Israeli analyst had claimed in Arabic on July 1st that Israel had attacked an Iranian uranium enrichment plant.
The BBC's Persian service, which Iranian authorities consider hostile, said it received a statement "hours before" the incident from a group called the "Homeland Cheetahs" who claimed responsibility.
They claimed to be "dissidents present in Iran's security apparatus" and said the location was targeted as it was not "underground" and that therefore the alleged attack could not be denied.
Iran's civil defence chief, Brig. Gen. Gholam Reza Jalali, told state TV on Thursday that any proven cyberattack against Iran would elicit "a response".
Israel's Defence Minister and Alternate Prime Minister Benny Gantz stayed ambiguous on the events.
"Iran is aiming for nuclear [weapons], we cannot let it get there," he said Sunday, but added that "not every event taking place in Iran is necessarily connected to us".
Explosion in industrial zone
Iran's official IRNA agency blamed human error for the Tuesday explosion at the factory south of Tehran.
The blast in "a completely industrial zone" of Baqershahr, 23 kilometres from the capital, was caused by "workers being negligent whilst filling oxygen tanks", it quoted the town's governor as saying.
"The explosion... was so powerful that the walls of the Saipapress factory nearby were also totally destroyed," Amin Babai said, without giving details on the function of the factory.
The incident took place inside the Oxijen factory, an emergency services spokesperson said, adding that all the casualties were male and that two of those wounded had been admitted to hospital.