WANA, Pakistan -- On a remote plain dotted with mud fortresses and ringed by steep mountains, Pakistani soldiers are waging their fiercest battle yet in the 2 1/2-year-old war against terrorism. At least 100 prisoners have been taken and casualties are mounting after five days of fighting between 7,000 Pakistani troops and an estimated 400 to 500 local Pashtun tribesmen and suspected foreign militants that showed no sign of abating Saturday. Pakistani officials now are backing down from speculation that the senior al-Qaida leader Ayman al-Zawahri is among the fighters hunkered down in a cluster of fortified mud-brick compounds west...