On the issue of Pakistan not letting the US talk directly to Khan, Tenet told NBC, "...Well, but, there's a great success because we, over eight years, we ended up taking down that network."

When pointed out that America and intelligence community still did not know where Khan sent his material, Tenet replied, "Well, we're working very, very hard at it.

"There are lots of places that we -- remember, al-Qaeda approached A Q Khan twice. Allegedly they were rebuffed.

We're now living in a world where networks of people pose threats to nation-states."

"In the Cold War, we were looking at big targets and big countries. Now we're looking at networks of people who seek to do us harm. And this issue I think is the most important issue we face," Tenet said.

The former CIA chief who has come out with his book At the Centre of the Storm: My years with the CIA is focus of a big debate over Iraq and his comments on the weapons of mass destruction of Saddam Hussein.

He was asked whether there are terrorist organisations that now have the capability of detonating a nuclear device in the United States.

"What I believe is, al-Qaeda is seeking this capability. You know, when we write about this, I take you back. (Osama) bin Laden, was looking for uranium in Sudan in 1993. He had a meeting with a non-governmental organisation of former Pakistani nuclear scientists in 2001 where crude weapons designs were shared," he said.