Hamas movement reiterated on Thursday that the Israeli Mossad was behind the killing of its drone engineer Mohammad al-Zawari in Tunisias second city Sfax last December. "Mossad is officially accused of being behind the assassination, which is not only a terrorist act, but a violation of state sovereignty," Mohammed Nazzal, a Hamas politburo member, said at a press conference in Beirut. According to Nazzal, Zawari’s assassination was meticulously planned over three stages in 2015 and involved 12 individuals. He said an investigation concluded that agents from Israeli intelligence agency Mossad had operated in Tunisia over several months, including pretending to be foreign journalists in order to get close to Zawari. The main two assassins who entered the country before the killing were using Bosnian passports, Nazzal said. Zawari, 49, was murdered at the wheel of his car outside his house in Sfax on December 15 last year.