 After being released he joined Fatah's Islamist rival Hamas' militant wing and was believed to have been involved in the bombing of a bus in Kfar Darom, following which he was arrested by the Preventive Security Force of the Palestinian Authority in 1998, being released the following year.In 2002, Jabari became the acting operational head of Hamas' military wing when Mohammad Deif was seriously wounded in an Israeli airstrike.In this position Jabari was also a high-ranking official within Hamas' political leadership, as well as the founder of the Nur Association, which aimed to help "martyrs and prisoners."