The International Atomic Energy Agency says it is making progress tracking down a global black market in nuclear technology that was run by a top Pakistani scientist. But the agency says it needs more information from foreign intermediaries and workshops that stored sensitive components.

U.S. and foreign officials say recent arrests and raids in South Africa, Germany and Switzerland mark a major breakthrough in unravelling the elaborate network, described by the IAEA as a "nuclear supermarket," that supplied Libya with its nuclear weapons program.

The network headed by Pakistani scientist Abdul Quadeer Khan, known as the father of the Islamic atomic bomb, had supplied countries such as Libya, Iran and North Korea with nuclear technology since the mid-1980s. In February he was dismissed from his government post and confessed on national television to leaking nuclear secrets.

Last week an IAEA team was in South Africa helping authorities follow leads on German businessmen for alleged nuclear trafficking on the Khan network. Shahram Chubin, director of research at the Geneva Center for Security Policy, says the South African connection comes as no surprise.

"If you've got a country like South Africa that had a fairly developed nuclear infrastructure and gave it up in the 1990s when it switched away from the apartheid regime, there must be quite a lot of expertise in the country both intellectual expertise and also equipment and technology," he said.

Mr. Chubin, who is Iranian, says after the end of apartheid, South Africa and Iran had good diplomatic relations that could have spilled over into sharing nuclear secrets.

"It's countries like Iran and South Africa that have been under sanctions for a long time, have had experience of sanctions and they've also had experience of breaking sanctions, which means front companies, third parties," he said.

Details of the nuclear black market emerged last year when Tripoli revealed it had purchased weapons designs from A.Q. Khan for around $50 million.

The IAEA learned that Dubai was a major shipping point for the transfer but that many companies, middlemen and financiers in Africa, Asia, Europe and the Middle East were involved in the manufacture, assembly and shipping of nuclear technology that could be used to make a bomb.

The news sent shockwaves throughout the UN nuclear agency which realised that any country with a fat check book could go on a nuclear shopping spree.

Designs Libya purchased from Pakistan, believed to be of 1960s Chinese origin, were apparently passed on to Tripoli in a simple dry cleaner bag.

Blueprints for nuclear weapons were given up by Libya this year, but analysts say these were copies of copies and the originals are still around somewhere. The Pakistani government denies knowledge of A.Q. Khan's illegal activities, but Rebecca Johnson, editor of Disarmament Diplomacy finds this hard to believe.

"I think it's highly implausible that the Pakistan government had not at least authorized Khan's activities in general even if they preferred not to know about the murky details," she said. "In my belief when we really find out more about the Khan network we will find commercial and military mercenaries from countries like South Africa and Britain".

A.Q. Khan was a metallurgist who had done postgraduate work in West Germany in the 1970s. He got a doctorate from the Catholic University of Leuven in Belgium and then started working with an Anglo-Dutch-German centrifuge enrichment partnership. In the mid-1970s he returned to Pakistan taking with him stolen centrifuge designs and a long list of companies supplying technology that could be used for nuclear weapons.

By the mid-1980s Mr. Khan had built up a network of middlemen and front companies and had imported enough highly enriched uranium for an atomic bomb. But analysts say he had imported too much and started to sell off the surplus on the international black market to countries like Iran.

He accumulated vast personal wealth, buying a hotel in West Africa and could command planes at his own disposal to dodge customs officials in delivering his secret consignments.

The IAEA is chasing up leads on suspected companies and individuals in about 20 countries including Malaysia, Sri Lanka, Russia, China, Spain, Turkey and Japan but says it needs more information and wants to carry out independent tests at locations in Pakistan.

So far Islamabad has refused and only given the IAEA samples taken by its own scientists.

The IAEA wants stiffer controls on nuclear material to prevent future Khans or terrorists from getting hold of the ingredients to make a bomb.

Gary Samore, former U.S. official and head of the International Institute for Strategic Studies, says this task will be difficult but not impossible.

"It's certainly too late in some respects, obviously countries that obtained technical information like Libya, Iran and North Korea, that is now in their possession, but it's not too late in the sense that it's still possible to make arrangements with those individual countries to persuade them to give up their nuclear weapons program, as the U.S. and the UK did with Tripoli, in their negotiations with Libya, and it's also still possible to close down the network so that it doesn't provide additional information to other countries," he said.

Next week the IAEA's 35-member board will review progress in doing this as well as tackling open questions on Libya and Iran's nuclear programs.