Worshippers had filtered into a mosque in northeastern Nigeria on Tuesday, mingling as morning prayers were just getting underway, when a suicide bomber detonated his explosives in the midst of the crowd. The blast in the town of Mubi was devastating, killing at least 50 people and leaving many others injured, according to local police.

"The roof was blown off," one witness, who lives nearby the house of worship, told the news service Agence France-Presse. "People near the mosque said the prayer was midway when the bomber, who was obviously in the congregation, detonated his explosives."

There was no immediate claim of responsibility — though it was immediately clear who authorities believe might have been behind the attack: Boko Haram, a militant Islamist group that grew out of nearby Borno state.

Boko Haram's jihadi fighters have been blamed for the deaths of roughly 20,000 people and the displacement of more than 2.6 million others in less than a decade. Just last week, the group was blamed for killing 14 people in the Borno state capital, Maiduguri, in what The Associated Press called "one of the largest such attacks in the city in years."

"We all know the trend," police spokesman Othman Abubakar told AFP. "We don't suspect anyone specifically but we know those behind such kind of attacks."

Adamawa, the state where Mubi is located, is no stranger to Boko Haram's violent attentions, according to NPR's Ofeibea Quist-Arcton.

"The extremists held territory in Adamawa state in 2014," she notes, "but were pushed out of the areas under their control by early 2015 in a concerted offensive by the Nigerian military, backed by troops from neighboring countries."

Late last year, Nigerian President Muhammadu Buhari announced the "long-awaited and most gratifying news of the final crushing of Boko Haram terrorists in their last enclave" — though it appears the year that followed has belied that declaration. A smattering of killings in Nigeria and Cameroon have been attributed to the group in the past few weeks alone.

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