Arms designs sold to Libya by top Pakistani scientist A Q Khan's proliferation network have been traced to China, providing clinching evidence of Beijing's involvement in Pakistan's nuclear weapons programme, media reports said.

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Bomb designs found in Libya last year by arms experts yielded dramatic evidence of China's long suspected role in transferring nuclear know-how to Pakistan in the early 1980s and assistance in production of its first nuclear bomb, The Washington Post said quoting government officials and arms experts.

"The Chinese designs were later resold to Libya by the Pakistani-led trading network that is now the focus of an expanding international probe," the Post said referring to A Q Khan's proliferation network.

The packet of documents, some of which included text in Chinese, contained detailed, step-by-step instructions for assembling an implosion-type nuclear bomb that could fit atop a large ballistic missile. They also included technical instructions for manufacturing components for the device, officials and experts said.

"It was just what you would have on the factory floor. It tells you what torque to use on the bolts and what glue to use on the parts," one weapons expert who had reviewed the blueprints told the Post adding the designs are "very, very old" but "very well-engineered."

US intelligence officials, the Post points out, concluded years ago that China provided early assistance to Pakistan in building its first nuclear weapon -- assistance that appeared to have ended in the 1980s.

Of the many proliferation activities linked to Khan's  network, the selling of weapons designs is viewed as the most serious.

The documents found in Libya contained most of the  information needed to assemble a nuclear bomb, assuming the builder could acquire the plutonium or highly enriched uranium needed for a nuclear explosion, the Post said.

Weapons experts familiar with the blueprints expressed surprise at what they described as wholesale transfer of sensitive nuclear technology to another country.

Notes included in the package of documents suggest that China continued to monitor Pakistani scientists on the finer points of bomb-building over a period of several years, the officials said.
 
A Q Khan stole the blueprints for centrifuges from Europe to refine uranium to bomb-grade material and China provided parts and know-how to make the bomb, the report said.

The package of documents was turned over to US officials in November following Libyan leader Moammar Gaddafi's decision to renounce weapons of mass destruction and open his country's weapons laboratories to international inspection.

The blueprints, which were flown to Washington last  month, have been analysed by experts from the US, Britain and
the International Atomic Energy Agency.
 
Weapons experts also found in Libya large amounts of  equipment used in making enriched uranium. The discovery helped expose the rogue nuclear trading network led by Khan that funneled technology and parts to Libya as well as Iran and North Korea.