The United States is seeking custody of Mr Ramzi Binalshibh, who is suspected of being involved in planning the September 11th attack.
Mr Binalshibh and at least nine other al-Qaeda operatives are being interrogated by Pakistani and US intelligence agencies four days after they were captured in a shootout in a residential area of Karachi.
President George W. Bush's national security adviser, Ms Condoleezza Rice, said: "We will be working with the Pakistani officials to make certain that he gets to the right place.
"There's no doubt that the United States will want to have access to him and to have him, because this is an important breakthrough".
One important obstacle to Mr Binalshibh's transfer to the US fell today when Germany decided not to pursue his extradition to face a mass murder-conspiracy indictment.
Germany had charged Mr Binalshibh with more than 3,000 counts of murder for allegedly conspiring on German soil to plan the September 11th attacks in the US.
Pakistan said a second high-level al-Qaeda figure was also captured last week, but has refused to identify him by name or nationality. There had been speculation the suspect was Khalid Shaikh Mohammed, one of Osama bin Laden's chief lieutenants.
PA