JOHANNESBURG (AP) — It is among Africa's most opaque security challenges: A campaign of attacks by mysterious militants in an impoverished corner of Mozambique that prompted a military crackdown, leaving civilians vulnerable in a cyclical conflict that has killed at least 100 people.

More than a year after insurgents announced their presence with a brazen assault on police in Cabo Delgado province, they have yet to clearly and publicly articulate what they want. The attackers have been described as Islamic extremists, but analysts say their ideology appears undeveloped and ethnic and economic resentments, as well as organized crime, could be key drivers of the unrest.

But the stakes are high because the Mozambican government hopes international plans to develop large reserves of natural gas in Cabo Delgado will eventually boost the economy.