The United States waged a secret diplomatic campaign in the 1970s to prevent Pakistan from developing nuclear weapons by pressing countries to control exports, declassified documents said.

In remarks with striking parallels to current US debates, officials in President Jimmy Carter's administration voiced fear about Pakistan's trajectory and tried both pressure and aid incentives to seek a change in its behavior.

In a secret November 1978 memo, then secretary of state Cyrus Vance instructed US diplomats in Western Europe, Australia, Canada and Japan to warn governments that Pakistan or its covert agents were seeking nuclear material.

Vance acknowledged that Pakistan was motivated by concerns over historic rival India. But he voiced alarm that Zulfikar Ali Bhutto, before being deposed as prime minister in a coup, said that Pakistan would share nuclear weapons around the Islamic world.

"We believe it is critical to stability in the region and to our non-proliferation objectives to inhibit Pakistan from moving closer to the threshold of nuclear explosive capability," Vance wrote, the year before the overthrow of Iran's pro-Western shah and the Soviet invasion of Afghanistan.

Britain was waging a parallel campaign, Vance said. Britain banned the export of inverters -- which can be used in centrifuges that produce highly enriched uranium -- and urged other countries to follow suit, Vance said.

Most countries sounded sympathetic, though West Germany -- a major industrial exporter -- insisted it already had adequate safeguards, memos said.

Pakistan nonetheless pursued nuclear weapons and detonated a bomb in 1998 in response to a test by India. The Pakistani scientist who built the bomb, Abdul Qadeer Khan, had access to sensitive technology in the Netherlands.

Khan admitted in 2004 that he ran a nuclear black-market selling secrets to Iran, Libya and North Korea. Khan, who is considered a hero by many Pakistanis, later retracted his remarks and in 2009 was freed from house arrest.

The declassified documents were released after requests by the National Security Archive at George Washington University and the Woodrow Wilson Center for International Scholars.

William Burr, a scholar at the National Security Archive, said that a US report from 1978 that could shed light on Khan's activities was missing and that he feared it had been destroyed.

The released documents said Pakistan wanted to maintain work on a reprocessing plant. France initially supported the project but backed out in 1978 due to fears that it would be used to produce weapons.

Then deputy secretary of state Warren Christopher in a secret memo urged a "low profile" on France's decision, saying it would "severely embarrass" France's then president Valery Giscard d'Estaing and impede future cooperation if it appeared he was responding to US pressure.

Christopher also said he was urging the US Congress to consider economic assistance and military sales to Pakistan, which was considered a US ally in the Cold War when India tilted toward the Soviet Union.

Assistance to Pakistan can "perhaps relieve some of the tension and sense of isolation which give Pakistan greater incentive to move covertly in the nuclear field," wrote Christopher, who later served as secretary of state.

The United States eventually pursued a major assistance package for Pakistan as part of a partnership against the Soviets in Afghanistan. The United States later cut aid due to nuclear concerns -- only to resume it again as it sought Pakistan's cooperation in Afghanistan following the September 11, 2001 attacks.

President Barack Obama's administration recently suspended about one-third of its $2.7 billion annual defense aid to Pakistan to put pressure for more action against Islamic militants.