Cambodia’s UN-backed genocide court has rejected an appeal by Khmer Rouge jailer Duch and increased his sentence to life imprisonment.Duch, born Kaing Guek Eav, was jailed in 2010 for his role in running a notorious prison where thousands of inmates were killed.He had appealed on the grounds that he was a junior official following orders.But judges rejected his claim and increased his sentence from 35 years to life.Duch - the first senior Khmer Rouge official to face charges before the court - was convicted of crimes against humanity in July 2010. He appealed against the verdict in March 2011.The 69-year-old was the commander of Tuol Sleng prison, where at least 15,000 men, women and children deemed enemies of the regime were tortured and then executed in "killing fields” outside Phnom Penh.He had argued that he should never have been tried, claiming that he was a junior official following his superiors’ orders on pain of death. Prosecutors, meanwhile, argued that his sentence was too lenient. Many survivors were outraged when he was sentenced to 35 years, because he could be free in 18 years given time already served.The appeal court judges ruled that the initial prison term did not "reflect the gravity of the crimes”."The crimes by Kaing Guek Eav were undoubtedly among the worst in recorded human history. They deserve the highest penalty available,” Judge Kong Srim said.