ABUJA, Nigeria – A female suicide bomber blew herself up outside the library of a government school in western Nigeria on Wednesday, killing herself and injuring three others, police said.

It was the first such attack in more than two years in the western state of Niger.

The girl or woman was inside the Federal College of Education at Katongora and approaching the library when the explosion went off around 12:45 p.m. Wednesday, said Police Deputy Superintendent Ibrahim A. Gambari.

Several previous attempts by female bombers have been bungled, leading to suspicion the bombers may be unwilling attackers and might be among hundreds of schoolgirls and young women kidnapped by Nigeria’s home-grown Boko Haram Islamic extremist group in recent years.

The group’s stronghold is in northeast Nigeria, where a suicide bomber on Monday killed 48 students and himself at an all-boys school in Potiskum, capital of Yobe state.

The pace and deadliness of attacks have increased since Nigeria’s military chief on Oct. 17 announced that Boko Haram had agreed to an immediate cease-fire to end a 5-year-old insurgency that has killed thousands and driven hundreds of thousands from their homes.

Boko Haram leader Abubakar Shekau has denied any truce and dashed hopes for the release of some 219 mainly Christian schoolgirls kidnapped from the northeastern town of Chibok in April.

No one knows how many dozens of other girls, women, boys and young men are held captive by Boko Haram, probably used as fighters, labour for transport and household tasks and as sex slaves.

Shekau said in a video last month that all the Chibok girls had converted to Islam and been married off to his fighters. The mass abductions provoked international outrage and criticism of President Goodluck Jonathan’s tardy response and the military’s failure to curtail the Islamic uprising.

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Faul reported from Johannesburg.