London, Sept. 12 : Fresh evidence has emerged that suggests Iran has renewed work on developing nuclear weapons.

The Telegraph quoted Western security sources as saying that American spy satellites have identified a number of suspicious sites, which the Iranians have not declared to nuclear inspectors.

Intelligence officials believe these are being used for covert research. They report having discovered enough enriched uranium, which if processed to weapons grade level, could be used to make at least six atom bombs.

They also say that about 50 to 60 tons of enriched uranium has disappeared from the main production facility at Isfahan.

The new discoveries emerged as it was revealed that Israel had asked America for military supplies, including "bunker buster" bombs and re-fuelling planes, suitable for an attack on Iranian nuclear installations.

The Israeli paper Haaretz reported yesterday that Israel has also asked for permission to use an air corridor through Iraqi airspace, currently controlled by America, to Iran.

So far the requests have been turned down by Washington, which is currently not as keen as Israel to consider a military strike against Iran.

The Isfahan complex enriches raw uranium "yellow cake" into material that can be used for either nuclear power or atomic weapons. Iran only allows IAEA inspectors access to the final stage of the production process where the uranium in gas form - UF6 - is stored.

IAEA officials believe the Iranians have deliberately removed the uranium at a stage in the production process that is not under their supervision.

Nuclear inspectors have also been concerned to discover that Gholamreza Aghazadeh, the head of Iran''s Atomic Energy Organisation, recently ordered scientists to increase the amount of UF6 being diverted from Isfahan to another storage facility.

IAEA officials have no idea where the missing uranium is being stored, but suspect it could be held at one of several suspicious installations that have been spotted by American spy satellites.

The Iranians will be asked to give a full account of the missing enriched uranium when the IAEA''s board of governors meets in Vienna later this month to discuss the continuing crisis over Iran''s nuclear enrichment programme. (ANI)