The United States is preparing to vacate Shamsi air base being used for CIA-operated drone attacks, a British report said Wednesday. US government sources reported that the US was preparing to accede to Pakistan's demand to vacate the air base. The move is not expected to have a significant impact on operations against militants. Following the NATO attack on a Pakistani military outpost last weekend that killed 24 Pakistani soldiers, Pakistan asked US to vacate the airbase besides suspending supplies to NATO forces in Afghanistan. Sources, who declined to be identified because of the issue's sensitivity, told news agency that U.S. planning was under way to leave the base, a remote facility in Baluchistan that has been a point of contention. The cross-border incident escalated tensions between the two countries and the U.S. military is conducting an investigation to find out exactly what happened on the ground.