Appearing before a Congressional hearing, Assistant Secretary of State for South and Central Asia Richard Boucher was asked if Khan had been questioned by US intelligence officials.

"I think we've said in public that we have not had direct access to Mr Khan, but we've had good cooperation from the Pakistani authorities," Boucher said before the Sub Committee on National Security and Foreign Affairs of the House Oversight and Government Reform Committee.

"We've had a good flow of information to the international community -- us, other countries, International Atomic Energy Agency -- and that we are confident that, based on that information, we've been able to put the network out of business," Boucher said.