The trip preceded the current probe into 12 top nuclear scientists, engineers and administrators, including the revered "father" of Pakistan's nuclear bomb Abdul Qadeer Khan.

The inquiry trip was prompted by a letter in November from the UN's nuclear watchdog, the International Atomic Energy Agency (IAEA), Information Minister Sheikh Rashid said.

"After the IAEA inquiries they wanted to have themselves some information against some people," Rashid said of the Pakistani team.

He said he did not know who was in the team or how large it was.

"They wanted to check how much involved (the scientists and engineers) were, whether they were involved or not."

Asked what they were alleged to be involved in, Rashid said: "something like information leakage."

Rashid would not say when the trip took place, but it appears to have been between the receipt of the IAEA letter in November and the first interrogations of nuclear scientists in December.

Three scientists, including the director of Pakistan's key uranium enrichment plant A.Q. Khan Research Laboratories, were taken in for questioning in December. Another eight were taken in at the weekend.

Even Khan himself, an official national hero, was also questioned though not in custody.

Three of those held in custody have since been cleared and released, Rashid announced Wednesday night.

Pakistan has been accused in a multitude of foreign newspaper reports quoting unnamed US, European and Middle Eastern officials, of proliferating nuclear technology to Iran, North Korea, and more recently Libya.

The government has vehemently denied any proliferation.

December was the first time it admitted that individual scientists were under suspicion.

Islamabad officials however insist any proliferation would only have been on an individual basis for "personal greed or ambition," and insists no government entity ever sold nuclear knowledge.

Iran and Libya are on the United States list of "rogue states" which support terrorism.

WAR.WIRE