"We believe that there's still some issues yet to be resolved with the A Q Khan network," Under Secretary for Intelligence and Analysis Charles Allen told lawmakers during a Congressional hearing.

"Fortunately, that network was severely disrupted and most of the people are no longer able to conduct that kind of activity. It was really becoming sort of the one-stop shopping for the provision of nuclear designs and centrifuges, as has been well publicised," Allen, also the Chief Intelligence Officer of the Department of Homeland Security, said.

"There are scientists around the world who may hold radical views -- the insider threat -- who might take materials or other kinds of hard, very complex equipment like centrifuges," he the Senate Committee on Homeland Security and Governmental Affairs Chaired by Senator Jospeh Lieberman.

"We have to have a regime that's not only here in the United States, which we do have, but worldwide to prevent these kinds of scientists who really become the rogue scientists," he said.