The United Nations special representative for West Africa says Nigeria's military needs to show "greater resolve" in the widening fight against the extremist group Boko Haram.

Mohammed Ibn Chambas told reporters Friday, "I think we all expect more from the Nigerian military."

His comments come after suspected Boko Haram militants staged their first attack in Chad.

Chambas says he hopes Nigeria will unite around fighting Boko Haram after presidential and legislative elections, delayed until March 28.

A multinational force to fight Boko Haram that also includes Chad, Niger, Cameroon and Benin is expected to be formally launched in coming weeks with about 8,700 troops. The force is expected to look to the U.N. Security Council for help in financing, but Chambas says he has heard no estimate of the cost.