The US knew of a network of nuclear proliferation from Pakistan for at least seven years before it was exposed, according to a report.

American, British and UN investigators found that a company in Pakistan was prepared to sell everything needed to make a nuclear bomb -- plans, equipment and fuel -- for $50 million, with no questions asked about how it might be used, it said.

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The package was even advertised at a Pakistani arms show in 2000, where the company handed out brochures to visitors, including a reporter for a defence weekly.

"The company gave out two very glossy brochures, inside of which they promised to provide all of the components needed for a uranium-enrichment facility," ABC News quoted reporter Andrew Koch as saying.

Pakistan's Nuclear Bazaar

Behind the programme was the now-disgraced Abdul Qadeer Khan, father of Pakistan's nuclear programme, who confessed last month to selling nuclear secrets to Iran, North Korea and Libya.

Investigators said he made millions running the operation.

"I think that now we have to confront the reality that there's a nuclear black market, a Wal-Mart, in effect, of nuclear smuggling and it covers four continents, a dozen countries, lots of inventive behaviour," said Graham Allison, director of Harvard University's Centre for Science and International Affairs.

Officials said it was a far-flung operation. A factory in Malaysia was set up to make the high-speed gas centrifuge parts used to produce weapons-grade uranium. Malaysian Prime Minister Abdullah Ahmed Badawi's son was one of the factory's owners.

"I did not talk with him on this subject. It is entirely my son's business," the network quoted Badawi as saying.

US officials said the key to the black market was a small, family-run company in the Swiss canton of St Gallen.

It was there, the officials told the network, that Swiss engineers helped design 14 key parts of the centrifuge sent to Libya to produce the uranium.

The Nigerian defence ministry said on Thursday that a top Pakistani general offered to help the African state "strengthen its military capability and acquire nuclear power", a claim Islamabad rejected as "unadulterated rubbish".