The US and Britain undertook a secret campaign in the late 1970s to prevent Pakistan from going nuclear and unsuccessfully tried to block its attempted covert purchasing of "gray area" technology for its atomic weapons programme, according to declassified documents.
According to the newly declassified state department cables, released by the National Security Archive, the US issued 300 demarches to Nuclear Exporters during 1978-1981 in attempt to halt Pakistani nuclear purchases.
At the same time, both Britain and the US kept India in the dark, even as Indian officials had better intelligence information about Pakistan's nuclear weapons programme.
The documents, however, do not mention the name AQ Khan, the National Security Archive said.
But already in late 1978 London and Washington were discovering the footprints of secret Pakistani purchasing organizations that were seeking the technology needed to produce fissile material -- plutonium and highly enriched uranium -- for nuclear weapons, it said.
In November 1978, Britain and the US sent complementary demarches to other members of the Nuclear Suppliers Group (NSG) in efforts to "delay" the Pakistani nuclear programme by denying it access to sensitive technology and equipment.
The US demarche was the first of about 300 sent over the next three years, it said, adding that the in its first such demarche, Washington was trying to halt a secret Pakistani effort to continue a plutonium reprocessing facility at Chashma, which the French had begun but had backed out of, partly in response to US encouragement.
The recently released state department records were once closely-held telegrams in the "NODIS" category.
"NODIS" documents are of such high sensitivity that they can only be read by a limited number of individuals with a specific "need to know."
Distribution and copying are strictly controlled by the state department's executive secretary, unlike the SIPRNet system exploited by Wikileaks, which allowed officials at far lower levels to decide on their accessibility.
These new unclassified document say after the French government cancelled the project at Chashma, they learned that the Pakistanis had begun a secret effort to acquire technology to complete the plant.
"The US role in cancelling the reprocessing plant caused resentment at high levels of the Pakistani government with military dictator General Muhammad Zia-ul-Haq asserting that US-Pakistani relations were at their 'lowest ebb'," said the National Security Archive.
"State Department officials wanted to move forward to restore more normal relations because they worried about the danger of a disintegrating or radicalised Pakistan and Islamabad's loss of confidence in Washington. Nevertheless, the restoration of economic and military aid could be jeopardized by evidence of a Pakistani nuclear program," it said.
"In response to Pakistani efforts to acquire inverters (or frequency converters), a 'gray area' technology used to regulate the speed of centrifuges for producing highly-enriched uranium, the British sent a demarche to members of the Nuclear Suppliers Group to seek agreement on preventing sales," the National Security Archive said.