Boko Haram fighters are massing at their headquarters in the northeast Nigerian town of Gwoza in preparation for a showdown with multinational forces, ABC News quoted residents and an intelligence officer as saying on Friday.
A woman trapped there since Gwoza was seized in July told her daughter that extremists are urging civilians to leave town to avoid being killed in crossfire in an anticipated major battle.
An intelligence officer said security forces are moving slowly for fear of harming civilians, and especially since Boko Haram is surrounding Gwoza with land mines.
He confirmed forces from Chad are in the area, speaking on condition of anonymity because he is not authorized to speak to reporters.
Boko Haram in August declared an Islamic caliphate across a swath of northeast Nigeria where it held sway. In recent weeks, Chadian and Nigerian troops have retaken a score of towns. But the militants continue to kill scores in suicide bombings and village attacks.