The largest chunk from this amount, $900 million, is available for reimbursement to Pakistan but almost half of it, $400m, has been put out of its reach. To get those $400m, Pakistan will have to get a 'good conduct' certificate from the US defence secretary.

Like a schoolmaster waiving the punishment given to a student, the defence secretary will have to certify that Pakistan is "taking demonstrable" steps against the Haqqani network of Afghan militants.

The measures also include a "sense of Congress that Dr Shakil Afridi is an international hero and that the government of Pakistan should release him immediately from prison".

Dr Afridi led US forces to the compound where Al Qaeda leader Osama bin Laden was hiding and is regarded in the Western world, particularly in the US, as an international hero.