Boko Haram extremists attacked a refugee camp in northeast Nigeria just days after Nigeria's air force bombed it, witnesses said Friday, as reports emerged that the death toll from the bombing could be as high as 170.

More than 100 Boko Haram fighters launched the attack Thursday evening, and soldiers battled for hours trying to repel them, witnesses said. One witness said eight Boko Haram fighters were killed and one soldier was injured, though others said the toll was still being determined.

The witnesses, who included aid workers and camp residents, spoke on condition of anonymity because of safety fears.

On Tuesday, Nigeria's air force bombed the camp housing Boko Haram refugees multiple times. The remote camp is located in Rann in Borno state, near the border with Cameroon.

Nigerian officials have said it was an accident - a rare admission.

On Friday, medical charity Doctors Without Borders said "around 90" people were killed in the bombing but noted that residents and community leaders say the death toll could be as high as 170.

Satellite imagery from the bombing supports witness accounts that the camp was struck with "multiple air-dropped munitions" even though tents should have been easily visible, Human Rights Watch said Thursday. The group has called for victims to be compensated.

Nigeria's air force has said a panel of senior officers will investigate.

The Boko Haram attack Thursday occurred as aid workers were trying to help bombing victims. The Red Cross said Thursday it had evacuated nearly 90 people from Rann to Maiduguri city for medical care.

"This incident happened just an hour after a (Doctors Without Borders) rescue helicopter left the town and has a traumatizing effect on everyone in Rann," said one aid worker.

Nigerian officials could not immediately be reached for comment.

AP