PARIS (Reuters) - France s efforts to combat terrorism and prevent further attacks on its soil are generating so much work for investigators and law courts that further staffing will be needed to keep up, intelligence and justice officials say. The warning comes at a time when President Emmanuel Macron is trying to curb public spending while ensuring security is not compromised, a balancing act that has already prompted an army commander to resign over budget cuts. The workload of the anti-terrorism justice system has risen ten-fold in the past five years, ministry figures show, with a sharp increase since 2014, when followers of the Islamic State group specifically called for attacks targeting the French. More than 240 people have been killed in the past three years in France, including 130 by a group of IS-inspired gunmen and suicide bombers in Paris in November 2015.  Statistics collected by the justice services underscore the scale of the judicial challenge.  In all of 2012, the year Islamist militant Mohammad Merah killed three Jewish schoolchildren and three soldiers near Toulouse - an attack now regarded as a turning point, there were 10 cases of suspected terrorist activity. In 2016, 240 new terrorism-related cases were opened, while in the first three months of 2017 a further 130 were added.  The total workload as of Oct. 9 was 621 cases, of which 452 were either early-stage or full inquiries into suspected Islamist-militant activity, according to justice officials. The number of counter-terrorist investigators at the Paris prosecutor s office has doubled since 2012, but still stands at only 14. Alongside them, the number of so-called investigating magistrates and judges dedicated to counter-terrorism has risen to 11 from 7-8, with another beginning next year.  We are not at breaking point, but the question now is how long it can last like that,  said Pascal Gastineau, head of the French Association of Investigating Magistrates. The workload is piling up in the courts as France cracks down on those who leave for Iraq and Syria to join IS, a number estimated at between 1,800 and 2,000. In the past, terrorism-related convictions meant around 10 years in prison. Now many of those who finance, recruit, join or return from the wars in Syria and Iraq face 20 years in jail. But convictions and the heavier sentences in most cases now require trial by jury of professional magistrates, a slow process that compounds the backlog.  For affairs dating to 2016, a trial will not take place before 2018-2019,  said one judge, who argues for some form of streamlining to process cases more rapidly. 