Phase III of the offensive began on 17 August and involved attacks in I, II and III Corps. Significantly, during this series of actions only North Vietnamese forces participated and targets were military in nature, with less concise attacks against city-targets. The main offensive was preceded by attacks on the border towns of Tây Ninh, An Lộc, and Loc Ninh, which were initiated in order to draw defensive forces from the cities. A thrust against Da Nang was preempted by the U.S. Marines' Operation Allen Brook. Continuing their border-clearing operations, three PAVN regiments asserted heavy pressure on the U.S. Special Forces camp at Bu Prang, in Quang Duc Province, five kilometers from the Cambodian border. The fighting lasted for two days before the PAVN broke contact; the combat resulted in US/ARVN claiming 776 PAVN/VC casualties, 114 South Vietnamese and two Americans.