The US State Department said on Thursday that it believes Libya's stockpiles of low-enriched uranium and mustard gas, built up by deposed leader Muammar Qaddafi, are secure, Reuters reports.
Department spokeswoman Victoria Nuland said the United States was monitoring sites where the stockpiles are held through its "national technical means" -- a euphemism for spy satellites and other intelligence assets -- and was confident of their security.
Nuland stressed that the main US weapons proliferation concern from Libya is the shoulder-fired surface-to-air missiles known as MANPADs.
The State Department announcement comes as reports emerge from Libya that US and British military commanders are seeking to determine the status of Libya's nuclear materials and chemical stockpiles.
Libya's uranium enrichment program was dismantled after Qaddafi renounced weapons of mass destruction eight years ago. Sensitive material and documentation including nuclear weapons design information were confiscated.
But the country's Tajoura research center near Tripoli -- with its 10MW research reactor -- continues to stock large quantities of radioisotopes, radioactive waste and low-enriched uranium fuel after three decades of nuclear research and radioisotope production.
"While we can be thankful that the highly enriched uranium stocks are no longer in Libya, the remaining material in Tajoura could, if it ended up in the wrong hands, be used as ingredients for dirty bombs," Olli Heinonen of Harvard University said.
"The situation at Tajoura today is unclear. We know that during times of regime collapse, lawlessness and looting reign."
A so-called dirty bomb can combine conventional explosives such as dynamite with radioactive material. Experts describe the threat of a crude fissile nuclear bomb, which is technically difficult to manufacture and requires hard-to-obtain bomb-grade uranium or plutonium, as a "low probability, high consequence act". This means it is unlikely to be used, but if the use does occur, it has the potential to cause large-scale harm to life and property.
Heinonen, head of U.N. nuclear safeguards inspections worldwide until last year, pointed to substantial looting that took place at Iraq's Tuwaitha atomic research facility near Baghdad after Saddam Hussein was toppled in 2003.
In Iraq, "most likely due to pure luck, the story did not end in a radiological disaster," Heinonen said.
In Libya, "nuclear security concerns still linger," the former deputy director general of the International Atomic Energy Agency (IAEA) said in an online commentary.
Libya's chemical agents are believed to have decayed over the years, and present more of an environmental hazard than a military one. Nor is Libya believed to have the means to turn its uranium yellowcake into highly-enriched uranium that can fuel a nuclear weapon.