Admiral Mike Mullen, the chairman of the US Joint Chiefs of Staff, has said that extremist groups that have launched attacks against US and Nato forces in Afghanistan "have been taking refuge across the border in Pakistan".

To fight that, Washington has been cultivating a relationship with the Inter-Sevices Intelligence (ISI), Pakistan's intelligence agency.

But as Imran Khan reports, the ISI are now facing their own struggle, as the Taliban turn on them.