John Bolton, the Under Secretary of State for Arms Control and International Security, has said that Washington has accepted the Pakistani government's information that small number of scientists were acting on their own, without the government's knowledge.
In an interview with San Francisco Chronicle, he said the United States is concerned that nuclear proliferation was taking place and a ring was involved in it.
Bolton refused to provide details or mention specific countries citing concern about sensitive intelligence but he said black-market rings trafficking in nuclear technology, parts and components are so wide and extensive that shutting them down even after the admissions by the scientists is proving to be an enormous challenge.
"One of the things that's been of concern for this administration from the beginning is the depth and complexity of the global black market in WMD (weapons of mass destruction) materials," he said.