Just heard on Naseem Zehra show on the TV (Nasim Zehra at 8PM) that the "Letter" in question is in fact a memorandum from Asad Qaiser detailing his assessment of the US -Pakistan relations which he gathered after meetings with the people in Washington. Assad Qaiser was our ambassador in the US until about 3 weeks ago when he was transferred.
The text of the "memo" may or may not be 100% correct because it is the inference of one person. Additionally, since the ambassadors report to the Foreign Minister, the possibility of it being written primarily for use a tool in the power politics cannot be ruled out.
I may be cynic in my old age, but this is a political war and " Everything is fair in love & war.