Armed militias in eastern Libya say they have found about two and a half tons of uranium ore that the International Atomic Energy Agency had reported missing, the BBC reported.
Ten barrels containing the ore were found near the border with Chad, the head of the force’s media unit said.
The IAEA said it was “actively working to verify” the media reports.
The agency sounded the alarm after its inspectors visited the undisclosed site earlier this week.
The area is not in government-controlled territory.
Uranium is a naturally occurring element that can be used for nuclear purposes after being refined or enriched.
The depleted uranium cannot be turned into a nuclear weapon in its current state, but could be used as feedstock for a nuclear weapons programme, experts have told the BBC.
In December 2003, under then-military leader Colonel Muammar Gaddafi, Libya publicly renounced nuclear, biological and chemical weapons and agreed to limit itself to possessing ballistic missiles with a range of no more than 300 km ( 186 miles).
But since the ouster of Colonel Gaddafi in 2011, the country has been divided into rival political and military factions.
It is currently divided between an interim, internationally recognized government in the capital Tripoli and another government in the east of the country.
Neither of them controls the southern part of the country, where the uranium was taken.
Thursday’s announcement that the barrels had been found was made by the self-proclaimed Libyan National Army, the military force that supports the administration in eastern Libya.
The LNA is a coalition of military units, local, tribal and Salafi militias led by Field Marshal Khalifa Haftar, a veteran officer who took part in the coup that brought Colonel Gaddafi to power in 1969.
General Khaled al-Mahjoub, commander of the LNA’s communications department, said the uranium containers were found “only five kilometers” from where they were stored in southern Libya.
The IAEA says the site has been difficult to reach in recent times.
Inspectors wanted to visit the site last year, but the trip had to be postponed because of fighting between rival Libyan militias.
Many foreign governments and groups have been jockeying for influence in Libya since NATO-backed forces ousted Colonel Gaddafi. Among them are the Russian group “Wagner” and the fighters of the “Islamic State”.
The oil-rich country is largely lawless and has previously been described as an “arms emporium”.
In 2013, the UN reported that weapons smuggled out of Libya were fueling conflicts in other parts of Africa and the Middle East.
The missing uranium was in the form of a concentrate known as “yellowcake” and “in its current form there really isn’t any radiation,” said Scott Reoker of the Nuclear Threat Initiative, a global security organization working on nuclear issues.
He told the BBC’s Newsday that there were fears it could be used as “raw material” for a nuclear weapons programme.
Mr Roecker suggested that it could potentially be used for other purposes, such as nuclear power, but pointed out that countries usually buy material for this purpose on the open market.
“Maybe it was stolen by someone who wanted to make a profit from it? There are many scenarios for that,” he said.