Boko Haram aims to establish an Islamic state in a country divided along Muslim and Christian lines. The country's president is a Christian.
A police source told the BBC at least 20 people, mostly students, were killed by gunmen in Mubi, a city with a mixed Muslim and Christian population. A resident told the BBC gunmen wearing military uniforms lined students up before the assault at a housing center near the Federal Polytechnic campus.
More than a dozen people were arrested on suspicion of allying with Boko Haram during military operations in Mubi last week. Nigerian authorities in response to this week's attacks imposed an indefinite curfew on the town.
Boko Haram didn't issue a claim of responsibility. The BBC reports mobile telephone towers were destroyed in the region by militant attacks so reporting is difficult. One eyewitness said the death toll may be as high as 40.
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