"That is a matter that the government of Pakistan is addressing," spokesman Scott McClellan said. "We appreciate their efforts to address what is a serious concern which is the proliferation of weapons of mass destruction."

Abdul Qadeer Khan, in a statement he read on Pakistan television, acknowledged he had "much to answer for" with regard to passing nuclear know-how to other countries and asked for forgiveness.

He said he accepted full responsibility for the nuclear transfers which he said were carried out "in good faith but on errors of judgement related to unauthorised proliferation activities."

The investigation was prompted by information from Iran that was forwarded to Pakistan via the UN's International Atomic Energy Agency (IAEA) in November.

"The government of Pakistan is continuing to look into issues of proliferation. There is an ongoing investigation in Pakistan related to proliferation issues and the government of Pakistan is still addressing these issues," McClellan told reporters.

WAR.WIRE