He also admitted: 'And yet the ISI has also served ... some very positive intelligence needs both in the country and certainly between our two countries. So, I think it's something we keep discussing, keep looking at. In the long run, it's about the security for Pakistan and better security in the region for both those countries.'

Mullen replied in the affirmative when asked if he believed the Al Qaeda leadership, including Osama bin Laden, is in Pakistan.

He added that the terror network Al Qaeda was 'at the top of the list' of his priorities and threats around the world.

While Mullen knows that Al Qaeda is based in FATA, the US troops are not in the area 'because FATA is in Pakistan and Pakistan is a sovereign country and we don't go into sovereign countries.'

Reminded of the examples of Iraq and Afghanistan, he said: 'And we don't go into sovereign countries unless we're invited in .... Afghanistan was a country from which the Al Qaeda leadership struck us and we responded.'