Pakistan 'apparently' helped China learn the secrets of a top US fighter jet at the height of the Vietnam War by allowing it to examine F-104s provided by Washington to Islamabad, according to secret US government documents made public in Washington.

The documents obtained by the National Security Archive, a private research agency, give an idea of the deep and longstanding strategic collaboration between China and Pakistan even when the US and Pakistan were wooing each other.

George C Denney, Deputy Director of Intelligence and Research said in a note to Secretary of State Dean Rusk on December 4, 1968 that the Johnson Administration would continue to be troubled by signs of close and highly secret cooperation between China and Pakistan.

Apparently, 'the Pakistani military had given the Chinese access to US F-104 supersonic fighter aircraft', Denny wrote quoting an intelligence source.

"Chinese technicians had been allowed to examine US-provided F-104 aircraft at Pakistan's Sargodha Air Base and to collect F-104 spare parts and material samples, which were taken back to China for analysis," he said.

He believed the action comes 'in violation of the acceptance agreement with the Pentagon. This generosity made the Chinese just as obliging in providing substantial interest-free loans (to Pakistan)', Denny wrote.

Denney also said China was willing to 'overlook ideological factors in dealing with Pakistan'.

The declassified papers show that by 1982, and probably earlier, the Reagan Administration had asked Chinese diplomats if Beijing was aiding Pakistan's nuclear programme, but was not getting any answers.

US Ambassador to Pakistan Arthur Hummel, in a cable in December 1982, reported that Chinese officials were unresponsive to US pleas for 'adequate safeguard' or other specific cooperation on nuclear exports. Moreover, 'the Chinese have also refused to give us an unequivocal answer that they are not assisting Pakistan's reported efforts to manufacture a nuclear explosive device'.

The US suspected China of making nuclear-related sales to Argentina and South Africa and providing 'weapons-related know-how to Pakistan'.

To control this problem as well as meet the US's own nuclear export goals, the embassy recommended greater nuclear cooperation: 'A US nuclear policy that will encourage China to keep in close touch with us on nuclear issues'.

This was part of the thinking that eventually led to US-China negotiations on nuclear cooperation that was formalised by a 1985 agreement, researchers say.

The revelation comes in the midst of a growing debate on a nuclear black market network run by top Pakistani metallurgist Abdul Qadeer Khan and how much authorities in Islamabad knew about it.

William Burr, editor of The National Security Archive, writes: "China's nuclear relationship with Pakistan was a matter of great concern to US government officials over the course of four presidential administrations.

"Since the early 1980s at least, allegations abounded that the Chinese government provided the Pakistanis with nuclear weapons technology, including design information. This assistance may have continued during the mid-1990s, or even later, though much remains conjectural."

"New evidence from Libya of Chinese language material among the nuclear weapons-design documents supplied by Pakistan raises new questions about the Chinese contribution to Pakistan's nuclear proliferation activities," the researchers say.

'Exactly what the US government knew and when it knew it remains highly secret in closed intelligence files, but the newly available diplomatic record shows' US unease over secret China-Pakistan security and military cooperation during the late 1960s, Chinese assistance to Pakistani nuclear-weapons related projects in 1977 and the refusal of Chinese diplomats in 1982 to give an 'unequivocal answer' to queries about nuclear weapons aid to Pakistan by China.

The documents also reveal the George H W Bush administration's concern in 1989 over 'reports of Chinese assistance to Pakistan's nuclear weapons programme', US pressure on China in 1992 to impose full scope safeguards on the sale of a nuclear reactor to Pakistan because of proliferation concerns and the

Clinton administration's 1997 certification of 'improvements in Beijing's nuclear proliferation policies'.

The Pak Nuke Bazaar