Iran is developing a second path to nuclear weapons capability by operating a plant that could produce plutonium, satellite images show for the first time.
The photos disclose details of activity at a heavily-guarded Iranian facility from which international inspectors have been barred for 18 months.
The images, taken only days ago, show that Iran has activated the Arak heavy-water production plant.
Heavy water is needed to operate a nuclear reactor that can produce plutonium, which could then be used to make a bomb.
The images show signs of activity at the Arak plant, including a cloud of steam that indicates heavy water production.
Inspectors from the International Atomic Energy Agency (IAEA) have been unable to visit the facility since August 2011 and Iran has refused repeated requests for information about the site, which is 150 miles south-west of the capital Tehran.
Western governments and the IAEA have held information about activity at Arak for some time.
But the images, obtained by the 'Daily Telegraph', are the first to put evidence of that activity into the public domain.
The details of Iran's plutonium programme emerged as the world's leading nations resumed talks with Tehran aimed at allaying fears over the country's nuclear ambitions.
The new images also show details of the Fordow complex, which is concealed hundreds of feet beneath a mountain near the holy city of Qom.
At talks in Kazakhstan yesterday, world leaders offered to relax sanctions on Iran in exchange for concessions over Fordow, which is heavily protected from aerial attack.
Iran insists that its nuclear facilities are for peaceful use, but Western governments fear that Tehran is seeking a nuclear weapon – or at least the ability to build one.
The striking image of steam over the Arak heavy water complex is a vivid demonstration that the regime has more than one pathway to a potential nuclear weapon.
Previously, international talks on Iran's nuclear programme have focused on Iran's attempts to enrich uranium at plants including Fordow.
But the new images of Arak highlight the progress Iran has made on facilities that could allow it to produce plutonium, potentially giving the country a second option in developing a nuclear weapon.
An Iranian bomb would allow the regime to survive any Western challenge and extend its influence in the Middle East.
Israel fears that a nuclear-armed Iran would pose a mortal threat and encourage more attacks on its territory by Hizbollah militants. (© Daily Telegraph, London)