Boko Haram has a well-defined organizational structure based on a fluid number of cells and hierarchical layers. It draws support from sympathetic Islamists in northern Nigeria; northern state institutions, including the government and security forces; and the Kanuri ethnic group, which accounts for roughly 4 percent of the country's population. Cross-state ethnic ties facilitate weapons trafficking, financial transactions and militant operations, including kidnappings. Abubakar Shekau, an ethnic Kanuri, is considered Boko Haram's leader. The group's highest decision-making body is known as the Shura Council. The council has about 30 members and has command over the group's various cells. Though this structure makes it difficult to define the actual size of Boko Haram, most estimates put its core membership at several hundred, excluding the large number of ethnically, ideologically or financially motivated supporters who participate in attacks or provide other forms of assistance.