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Asbel Kiprop tested positive for the endurance-boosting drug EPO, the Athletics Integrity Unit (AIU) confirmed on Friday, refuting allegations by the Kenyan track star that his sample might have been contaminated. Kiprop, a three-time world 1500m champion and 2008 Olympic gold medallist, on Thursday "vehemently denied" doping, suggesting an out-of-competition sample he gave could have been contaminated by two anti-doping agents he suspects might have targeted him for extortion.