WASHINGTON, March 6: Newly declassified US government documents made public on Friday speak of almost three decades of US unease over China's alleged cooperation with Pakistan over its nuclear weapons programme.

One of the briefing papers released on Friday states: "We have concluded that China has provided assistance to Pakistan's programme to develop a nuclear weapon capability" in the areas of fissile material production and possibly also in nuclear device design.

Researchers who obtained the documents and made them public said that exactly what the US government knew about the alleged Chinese nuclear sharing with Pakistan remains highly secret.

But the newly released cables and memos provide specific details on how US officials looked at the China-Pakistan relationship, how they persistently tried to discourage it and how Chinese diplomats repeatedly denied any involvement, said William Burr of the National Security Archive, a research institute at George Washington University.

The material obtained by the Archive under the US Freedom of Information Act run from 1965 through 1997 and discusses US concerns about China-Pakistan security and military cooperation dating back to the mid 1960s.

The documents' release comes at a time of great interest in proliferation because of revelations by Dr Abdul Qadeer Khan.

Mr Burr said that until the revelations from the Libyan files, "no evidence had surfaced that conclusively linked China with Pakistan's nuclear weapons programme".

However, the Bush administration, which boasts that US ties with China have never been better, has played down the Chinese nuclear connection.

Undersecretary of State John Bolton, the top US arms control official, said on a visit to Beijing two weeks ago that despite alleged sales of nuclear-related technology in the past, China now seems to be cooperating with the United States to prevent proliferation.

In a 1983 State Department briefing paper, the writer begins: "There is unambiguous evidence that Pakistan is actively pursuing a nuclear weapons development programme."

Even then, the Americans knew that "technology obtained by Pakistan in Europe has provided the base for the development of the new labs" yet they suspected Chinese cooperation.

In 1996, during the Clinton administration, Beijing made a public declaration that it would not assist nuclear facilities like Islamabad's.

But CIA Director George Tenet, in a report covering the period as recently as June last year, said his agency could not rule out continued contacts between China and Pakistan on the nuclear issue.-Reuters