Attacks on schools, churches

But when the armed men started ransacking the school stores and set fire to the building, the terrified girls being herded at gunpoint into vehicles realised they were being kidnapped.

"We were crying," Isaiah said, recounting how she later jumped from a truck and ran away to hide in the bush. Other girls were packed into a bus and some pick-ups.

Boko Haram, which in the Hausa language broadly means "Western education is sinful", has previously attacked several schools as symbols of secular authority, killing pupils and teachers, as well as Christian churches and Nigerian state targets such as police, army and government offices.

Chibok is not far from a rugged area of forest, hills and caves where military officials say Boko Haram has camps near the border with neighbouring Cameroon. They have abducted girls in the past to be sex slaves for the fighters and to do camp work.

No one has claimed responsibility for the abduction or for the rush hour bomb blast on Abuja's outskirts, which put the capital on alert around three weeks before the central city was due to host a high-profile World Economic Forum on Africa.

But President Jonathan has pointed the finger of suspicion for the bombing at Boko Haram, bringing home to Nigerians in the centrally-located capital that the Islamist insurrection ravaging poorer states hundreds of kilometers (miles) to the northeast could also strike much closer to home.