Taliban war Base Connolly, Afghanistan: US Defense Secretary Robert Gates told US troops in Afghanistan their sacrifices were paying off Tuesday, ahead of a key strategic review of the nine-year war. He flew in on the previously unannounced visit amid further tensions between Washington and Kabul after leaked American diplomatic cables offered a scathing account of Karzai and his corruption-tainted allies. Last December US President Barack Obama ordered 30,000 extra American troops into Afghanistan and renewed efforts to build up Afghan security forces as part of a sweeping strategy shift designed to hasten an end to the fighting. In the eastern province of Nangarhar, Gates thanked troops from the 101st Airborne and expressed sympathy over recent deaths after six Americans were killed last week by an Afghan border policeman during a training session. It was the deadliest attack of its kind by insurgents who have infiltrated Afghan forces, which threaten to undermine a key plank of the US war strategy. “I know you all have had a rough go of it,” and taken “a lot of losses”, Gates said. But he said the sacrifices were “worth it”. “What you're doing is incredibly important,” he said. His spokesman Geoff Morrell earlier said that Gates arrived “feeling very good about the progress that has been made in the past year” and said the visit would help shape a war strategy review under way in the White House. Gates was scheduled to hold talks with Afghan President Hamid Karzai and the top NATO commander in Afghanistan, US General David Petraeus, who expressed doubts Monday about the prospect of a victory in Afghanistan by 2014. Gates also visited troops in the eastern province of Kunar on Tuesday. Meanwhile, British Prime Minister David Cameron said Tuesday during a surprise trip to the country that British troops may start withdrawing from Afghanistan in 2011. Since taking office in May, Cameron said his government had scaled back British ambitions in Afghanistan and acknowledged the dangers of waning public support. He also said British troops will quit their combat role in Afghanistan by the end of 2014. “The whole of NATO have signed up to a transition process that starts early next year handing over districts and provinces to Afghan lead control, to be completed by 2014,” Cameron said Tuesday at a news conference with Afghan President Hamid Karzai. Afghanistan's foreign minister “expressed disappointment in the British, contending they were not ready to fight as actively as American soldiers.” Cameron responded Tuesday that “it's clear now that we didn't have enough troops in Helmand,” a southern province and Taliban stronghold. Karzai brushed off the controversy, as well.