Amnesty said it had verified the information about the abduction with "credible sources".
"Amnesty International has confirmed... that Nigeria's military headquarters in Maiduguri was aware of the impending attack soon after 7:00pm (6:00pm GMT) on 14 April, close to four hours before Boko Haram began their assault on the town," the group said.
The military however could not assemble the troops needed to suppress the attack, "due to poor resources and a reported fear of engaging with the often better-equipped" Islamists, according to Amnesty.
The 17 army personnel based in Chibok were overpowered by the attackers and had to retreat, the London-based group further said.
"The fact that Nigerian security forces knew about Boko Haram's impending raid, but failed to take the immediate action needed to stop it, will only amplify the national and international outcry at this horrific crime," said Netsanet Belay, Amnesty International's Africa director for research and advocacy.