PARIS - Pole vault legend Sergey Bubka admitted Sunday he was “shocked” by claims of widespread doping amongst Russian athletes and pledged a crackdown on the “criminal” gangs who control the drugs supply. Russian officials have strongly denied claims of state-backed doping made in a German TV documentary while the country’s athletics federation has said it is considering legal action. Bubka described the allegations in the ARD/WDR documentary as “very serious”. “I am deeply shocked and understand that we need to act quickly and transparently now in order to protect the integrity of our sport,” he said. “I believe in a zero tolerance policy against doping and we have to consistently and relentlessly fight against what is the biggest threat to sport in the 21st century.”