WASHINGTON (Online) - Pakistans decision to evict the United States from a Predator drone base will have little impact on the CIAs ability to strike terrorists in the countrys austere tribal areas because the US has built backup bases in Afghanistan, a senior US defence official has said. The official told The Washington Times that the US military and CIA had built the launching strips in Afghanistan in anticipation of the day when Pakistan wanted US forces out of the Shamsi facility. Shamsi is widely understood to be the base of operations for the covert CIA drone war on terrorists in tribal areas. Pakistan ordered the United States to leave the Shamsi base and shut down a vital supply line to Nato troops in Afghanistan after coalition forces airstrikes killed 24 Pakistani soldiers in a border clash on Nov 26. President Obama on Sunday expressed condolences for the deaths of the Pakistani soldiers in a phone call to Pakistani President Asif Ali Zardari, the White House said in a statement. Mr Obama made clear that this regrettable incident was not a deliberate attack on Pakistan and reiterated the United States strong commitment for a full investigation, the statement said. Both presidents reaffirmed their commitment to the US-Pakistan bilateral relationship, which is critical to the security of both nations, and they agreed to stay in close touch, the White House said. The defence official, who asked not to be named because of the issues sensitivity, said the administrations view is that Pakistan announced the eviction of the drone operation to placate political and Islamic groups. They are dealing with multiple audiences, the official said. Defence Secretary Leon E Panetta, while CIA director in 2009, had revealed that the Predator strikes in the tribal areas represented the only way for the United States to kill Qaeda and Taliban targets because Pakistan would not allow any expanded ground or air assaults by American forces. The Predators importance, and shaky relations with Islamabad in recent years, prompted the CIA to ratchet down operations at Shamsi and launch more flights from Afghanistan. We have many redundancies, the official said. We like to have multiple ways of doing things. Its not a big issue that would mean any huge degradation. At one time, the CIA launched Predators from at least two bases in Pakistan. Pakistan realises that there are terrorists who threaten its regime. For that reason, Islamabad wants the US to continue Predator attacks, the senior official said. Pakistan also does not want to further jeopardise the huge amount of economic and military aid the United States sends its way