Russian President Vladimir Putin demanded on Saturday that the United States shows proof that the Syrian regime used chemical weapons, arguing that failure to do so would mean that none exists. \"Regarding the position of our American colleagues, who affirm that government troops used... chemical weapons, and say that they have proof, well, let them show it to the United Nations inspectors and the Security Council,\" he told journalists. \"If they don\'t show it, that means there is none.\"