The top spokesman for Nigeria's military says officials believe Islamic extremists fighting in the nation's restive northeast are receiving arms and other assistance from sources outside of the country.

Brig. Gen. Chris Olukolade told The Associated Press on Thursday that the types of arms being used by extremists appeared to come from outside of Nigeria and represented a significant shift in materiel compared to the light weaponry the militants previously used. Olukolade showed AP journalists an image of what he described as a shell from an anti-aircraft gun mounted to the back of a pickup truck — weapons previously unseen in Nigeria's long-simmering Islamic insurgency.

President Goodluck Jonathan has declared emergency rule in three states in the northeast, allowing soldiers there to arrest anyone and occupy any building.