Witnesses and police say a military helicopter crashed in an explosion of fire near a college hostel in northeast Nigeria, where troops are fighting an Islamic insurgency. They saw no survivors.

Four days earlier, the military reported a helicopter safely crash-landed in the area. Two months ago, Islamic extremists said they shot down a fighter jet and published video showing the beheading of a man friends identified as a Nigerian Air Force pilot.

The United States said Wednesday it refused to sell Nigeria attack helicopters partly because of concerns it could maintain the aircraft.

Police spokesman Othman Abubakar confirmed the crash in Yola, capital of Adamawa state, but gave no details.

Witness Habu Mallam said it fell in a ball of fire around midnight Thursday.