(.) By Julien Pretot PARIS, March 29 (Reuters) - Cycling's authorities are under pressure to improve safety after Belgian rider Antoine Demoitie died following an accident involving a motorbike on Sunday but it will be a tough task in a sport which is still largely amateur. While the International Cycling Union (UCI) expressed its sadness over Demoitie's death on Monday without discussing the circumstances of the accident, the riders' association (CPA) has demanded a probe and improved safety measures. Slovakia's Peter Sagan and Portuguese Sergio Paulinho were sent crashing to the ground by motorbikes during last year's Vuelta, while Belgian Greg van Avermaet, who was soloing towards victory, was dismounted by a motorbike at the Clasica San Sebastian. More...