Pakistani soldier near the Pakistan-Afghan borderSpeculation the United States is preparing to send commandos into Pakistan’s tribal areas to hunt down al Qaeda and Taliban militants is gathering momentum.  Pakistani fears of a U.S. attack were reinforced by a surprise visit to Pakistan this weekend by the Chairman of the U.S. Joint Chiefs of Staff, Admiral Mike Mullen, in which he was reported to have expressed U.S. frustration that Islamabad was not doing enough to tackle militants on its border with Afghanistan.