When in the fall of 2017 random attacks by unknown groups on populated areas in the northern Mozambique in the province of Cabo Delgado began, it was assessed as «incidents of criminal nature» inspired from abroad. Few could have foreseen that these events would lead to a major Islamist insurgency that has engulfed nearly half of the province over the past few years. Young local people belonging to the Islamic radical sect, which arose on the wave of dissatisfaction with the socio-economic situation in Cabo Delgado, managed to organize themselves in gangs and began to spread militant ideology to neighboring areas. In a relatively short time, this group called «Ansar al-Sunna» was able to take control of the drug trade and smuggling, which provided the group with funding, development and reinforcements. The article deals with the transition of an illegal armed group to large-scale terrorist activities against the civilian population, which led to a humanitarian crisis. By early 2021 this group has become a large well-armed and equipped formation of several thousand fighters on whose side hundreds of militants from various states from Asia and Africa are fighting and has established ties with the terrorist organization ISIS. The article examines the causes of the rebellion, its growth and transformation into a simmering regional conflict. The author analyzes the course of hostilities and the efforts of the government of Mozambique to contain the uprising. The author also assesses the regional and global threats to which this conflict may lead, including the spread of the conflict to other states, maritime security, increase of drug-trafficking and the possible shutdown of gas production that is vital for Mozambique economy.