China had tested for Pakistan its first nuclear bomb as early as in 1990, enabling Islamabad to respond within weeks to the Indian atomic tests eight years later, a top US nuclear expert has claimed.

"The Chinese did a massive training of Pakistani scientists, brought them to China for lectures, even gave them the design of the CHIC-4 device, which was a weapon that was easy to build a model for export," former US Air Force Secretary Thomas Reed told American news magazine 'US News and World Report'.

Reed, who had worked at Livermore National Laboratory as a weapons designer, had co-authored a new book -- The Nuclear Express: A Political History of the Bomb and Its Proliferation -- with Danny Stillman, the former director of the technical intelligence division at Los Alamos National Laboratory.

The book makes a scathing indictment of China, alleging that it intentionally proliferated nuclear technology to ‘risky regimes’, particularly Pakistan, the magazine said.

The Chinese gave the nuclear technology to Pakistan as ‘India was China's enemy and Pakistan was India's enemy,’ Reed told the magazine.

"Under Pakistani President Benazir Bhutto, the country built its first functioning nuclear weapon. We believe that during Bhutto's term in office, the People's Republic of China tested Pakistan's first bomb for her in 1990," he said.

He said there are numerous reasons to believe this, including the design of the weapon and information gathered from discussions with Chinese nuclear experts.

"That's why the Pakistanis were so quick to respond to the Indian nuclear tests in 1998. It only took them two weeks and three days," Reed said.