WASHINGTON, March 9: US Secretary of State Colin Powell described Dr A.Q. Khan on Tuesday as "the biggest nuclear proliferator ever" but rejected allegation that the United States let him off the hook to please Pakistan.

In two separate television and radio interviews, Mr Powell defended President Pervez Musharraf's decision to pardon Dr Khan as a move that allowed the US to learn as much as it could about his network.

"There are questions about why the United States didn't come down harder on Pakistan for the actions of Dr Khan, arguably the biggest nuclear proliferator ever? Did the US administration just ignore this, as some contend," Mr Powell was asked.

"No, we didn't ignore it at all. He was, perhaps, the biggest proliferator ever. He is not any more. And the US provided information and intelligence to President Musharraf as to the nature of Dr Khan's activities, and we worked with President Musharraf to make sure that all of these activities became public and were taken into account, and action was taken. And what President Musharraf did was confront Dr Khan and his associates, interrogate them, get the information, cause Dr Khan to go on public television and acknowledge what he had been doing over these years, and we are getting a steady stream of information as to the nature of that network; and the network's being pulled up. And you can see the results already in places like Libya and in other countries," said Mr Powell.

Dr Khan is a very prominent figure in Pakistan who is considered a national hero because he helped Pakistan develop its nuclear weapons some years ago, said Mr Powell while explaining why President Musharraf had to pardon him. "And so President Musharraf, having destroyed the Khan network and causing Dr Khan to acknowledge his efforts, has decided that he had to offer to Dr Khan a conditional amnesty, conditional meaning that it can be taken away," he added.

"So we continue to get information. Our goal was to destroy the network, and the network is destroyed and all elements of that network are being ripped up; all of its roots and branches are being pulled up and cut down. And what ultimately happens to Dr Khan is a matter for the Pakistanis to decide."

Rejecting the suggestion that the US was too mild in dealing with Pakistan on this issue, Mr Powell said: "We came down very, very firmly with the Pakistanis on the need for them to help us and to help themselves totally pull up that network, and that's what the Pakistanis have done."