DAMATURU, Nigeria — Yobe state governor's spokesman says soldiers guarding a checkpoint near a government school mysteriously withdrew hours before a pre-dawn attack in which suspected Islamic extremists killed at least 29 students.

A teacher said the militants struck before dawn Tuesday and locked the door of a dormitory where male students were sleeping and then set it ablaze, slitting the throats of students who tried to clamber out of windows and gunning down those who ran away. He said some students were burned alive.

Spokesman Abdullahi Bego said Gov. Ibrahim Gaidam will ask why the school apparently was left unprotected. He said the governor visited the deserted remains of Federal Government College at Buni Yadi, a secondary school, and was told the soldiers withdrew Monday.