The study aims to evaluate the safety and clinical effect of daily oral treatment of Laquinimod capsules in active moderate to severe Crohn's disease. This study will assess Laquinimod doses of 0.5mg /day to 2 mg/day in sequential dose groups (cohorts). Laquinimod is a novel immunomodulating drug which is currently in advanced stages of development by Teva Pharmaceuticals Ltd. for Multiple Sclerosis.