ABUJA, Nigeria — Gunmen attacked a high school in northwestern Nigeria before dawn on Monday, taking 25 schoolgirls and killing at least one staffer, authorities said of the latest abduction of students in the region .

No group immediately claimed responsibility for abducting the girls from the boarding school in Kebbi state and their motivation was unclear.

Nigeria is facing a multidimensional security challenge , specifically from amorphous groups of armed bandits who specialize in kidnapping for ransoms — sometimes totaling thousands of dollars — and have been responsible for several high-profile abductions across Nigeria’s northern region. Kidnappings, attacks on villages and along major roads have become common because of the limited security presence.

Those bandits are not c

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