The UN’s nuclear watchdog, the International Atomic Energy Agency, has said 10 drums of concentrated uranium ore are missing from an undisclosed site in Libya.
The finding, described in a document seen by Reuters, said 2.5 tonnes were no longer present at a site where they had previously been listed.
UN inspectors visited Libya in 2003 when the country gave up its weapons of mass destruction (WMD) programme, after the US invasion of Iraq, when the US and UK incorrectly said Iraq possessed WMDs.
The UN watchdog said the “natural uranium” was in the form of uranium ore concentrate, which is stored in tightly sealed steel barrels that typically weigh around 350kg.
The concentrated ore has to be processed using dangerous chemicals to be turned into liquid form, before it solidifies into uranium that can be further enriched.
In the latter process, it is turned into a gas before being further enriched using centrifugal force, in devices known as centrifuges.
IAEA chief Rafael Grossi told the organisation's member states that inspectors found the drums were “not present as previously declared” at the location in Libya.
The IAEA will conduct further activities “to clarify the circumstances of the removal of the nuclear material and its current location”, it said.
Estimates vary as to how much concentrated uranium ore is needed to build a nuclear device.
Removing uranium-235 — the chemical element required for further enrichment until it becomes pure enough to make a bomb — is a complex process.
How much of the heavy metal that can be extracted from the ore depends on the efficiency of the equipment used in the process.
About 0.7 per cent of uranium ore is U-235 and about 50kg of highly enriched uranium is required for a bomb.
Many tonnes of concentrated uranium ore would be needed to start the process of enrichment to “weapons grade”.