The UN's nuclear agency has voiced concern at recent revelations about a sophisticated international illegal trade in nuclear technology.
The scale of Libya's nuclear programme took many aback
It was clear a multitude of countries and companies were involved and the supply must be stopped, said the International Atomic Energy Agency.
IAEA inspectors are now in Libya checking details of the nuclear weapons programme it recently acknowledged.
An IAEA spokesman said the black market had aided Libya in its programme.
The inspectors are making an inventory of all materials connected with the programme, said agency spokesman Mark Gwozdecky in Vienna.
IAEA teams are in charge of sealing sensitive material, including nuclear bomb designs, turned over by Libyan scientists.
Access to items placed under the agency's seal, said the spokesman, was dependent on the IAEA's agreement.
Mr Gwozdecky described the nuclear black market as a "real eye-opener".
He added that the IAEA's inspectors were working closely with US and British officials despite recent strains in their relations over the role the agency should play in Libya's disarmament.
The White House announced earlier this week that components of Libya's nuclear weapons programme had been flown to the US.
Materials including uranium hexafluoride and centrifuge parts were flown to Knoxville, Tennessee, on a US transport plane on Monday.
A total of about 25 tons (55,000 pounds) of equipment and documents were transported.
White House spokesman Scott McClellan said the move showed "real progress" towards Tripoli's disarmament, although it was too early to discuss the lifting of US sanctions on Libya because there was "more to do".
A US-Libyan thaw began after Libyan leader Colonel Muammar Gaddafi announced on 19 December he was abandoning efforts to acquire weapons of mass destruction and opening facilities to international inspectors.
US and British teams have since visited sites, while the IAEA has dispatched its own inspectors, including centrifuge and weaponisation experts.