The BBC reports that the Pakistani embassy in Kabul has been sacked by a mob protesting about supposed Pakistani interference in Afghanistan. Worse, there have apparently been several frontier incidents between Pak and Afghan troops, including exchanges of fire. The Afghans have every reason to suspect and fear Pakistani machinations in their country - the Inter-Service Intelligence Agency, through the Pakistani policy of seeking "strategic depth", was famously deeply involved in the creation of the Taliban movement, backing Gulbuddin Hekmatyar in the civil war and even, some say, plotting to hide Pakistani nuclear arms in Taliban territory in the event of war with India as a kind of cheap second strike capability.
Since Sep. 11 2001 and the beginning of the current world crisis, Pakistani soldiers have been sent into the tribal areas on the Northwest frontier for the first time in an effort to subdue al-Qa'ida activities up those mountains. Reports of mysterious western special-force people (CIA operatives? Green Berets? UK or Aussie SAS?) have not been uncommon - one hopes the Americans have not been foolish enough to encourage Pakistani forces on these operations to cross the border. Even US or British soldiers might not be as unpopular as Pakistanis there, as evidenced by the embassy riot.