'Blast' deepens mystery of Iran's Parchin military complex
Mystery surrounds reports of an alleged explosion or fire at the secret Parchin military complex in Iran on Sunday.
Recent satellite photos analysed by experts from the Institute for Science and International Security (ISIS) suggests some damage at the site, giving additional credence to the reports.
Parchin, south of the capital Tehran, is the location of a facility where Iran is suspected of having conducted high-explosive tests related to the manufacture of nuclear weapons.
The global nuclear watchdog, the International Atomic Energy Agency (IAEA), has not had access to the site since 2005.
The facility is important because what may or may not have happened there is crucial to unravelling Iran's past nuclear activities. And unravelling what may have happened in the past is central to resolving the outstanding issues surrounding its nuclear programme today.
For Mark Fitzpatrick, director of the non-proliferation and disarmament programme at the International Institute for Strategic Studies (IISS) in London, Parchin is a key piece of the jigsaw.
"It's important for the IAEA to get into Parchin in order to try to resolve the allegations of nuclear weapons-related experiments that were said to have taken place there," he says.
"The timeline is of particular interest. Most of the reports of nuclear activities of a 'possible military dimension' that the IAEA is trying to run down took place before Iran's weaponisation work was mostly suspended in late 2003, but experiments at Parchin reportedly continued after that date."
Iran of course denies that it carried out any work related to a nuclear bomb at Parchin. But over recent years a series of ISIS reports have shown suspected sanitisation activities going on at the plant.
Pride and politics
The allegation is that Iran has been pursuing a comprehensive programme to remove evidence of nuclear-related activities. Buildings have been demolished, while the rubble and connecting roads have been removed or erased.
Satellite images going back to 2012 show earth-moving equipment and water tanks at the facility. Meanwhile, images from 2013 show large areas of ground that have been covered by asphalt.
Mr Fitzpatrick says: "Given the clean-up efforts that have apparently been underway since the IAEA in early 2012 sought to go back to Parchin, it is unlikely that the IAEA would be able to find any incriminating evidence there.
"It is therefore mysterious why Iran has steadfastly refused access - after having tentatively agreed in 2012 to allow it. "
Mr Fitzpatrick says the answer is probably related to "pride and internal politics", adding: "The hardliners do not want to grant any concessions unless Iran is suitably rewarded."
The reports of a recent fire or explosion at Parchin have only added to the mystery.
Imagery obtained by ISIS show buildings that have been destroyed or removed and at least one that has been damaged. They also seem to show evidence consistent with a large explosion.
So what is going on? Mark Fitzpatrick has his theories.
"After all the attention on Parchin, it's unlikely that Iran would still be using it for nuclear weapons-related work - if indeed it was ever so being used.
"If, on the other hand, Iran was developing nuclear weapons there and refused inspections, then it would be a prime target for a pre-emptive military strike. That's why there was so much interest when a large explosion was reported at Parchin.
"But so far there is no evidence that the explosion took place at facilities suspected of being involved in nuclear efforts."