ADDIS ABABA, Ethiopia — The threat posed by Boko Haram, Nigeria's Islamic extremist rebels, will be a focus of U.N. Secretary-General Ban Ki-moon as he attends the African Union heads of state summit in Addis Ababa, Ethiopia, a spokesman said.

The U.N. chief will be encouraging officials in Addis to find a solution to the Boko Haram violence, Stephane Dujarric, told reporters late Wednesday in New York.

Boko Haram is increasing its attacks as Nigeria prepares for Feb. 14 elections. Thousands have been killed in the 5-year insurgency.

Hiroute Guebre Selassie, the U.N. Special Envoy for the Sahel region in Africa, earlier said she is concerned that Boko Haram's violent campaign could destabilize West Africa if current trends continue.

The Islamic extremists were reported this week to be rampaging through villages in northeastern Nigeria, killing, burning and looting with no troops protecting civilians, fleeing villagers said Wednesday. More than 40 people have been killed in seven villages in the attacks that started Friday.