Story highlights Attack happened at height of business at weekly market in town of Biu in Borno state

No claim of responsibility was immediately made

Northeastern Nigeria has long been scene of attacks by Boko Haram

Kano, Nigeria (CNN) A female suicide bomber attacked a crowded market in northeastern Nigeria's Borno state on Thursday, killing seven people and seriously injuring 20 others, residents and a hospital source said.

The bomber, wearing a hijab, detonated her suicide vest in the midst of shoppers at a weekly market in the town of Biu around 3 p.m. at the peak of business, witnesses said.

"We have evacuated eight bodies, including that of the bomber, to the hospital along with 20 people injured in the attack," Bukar Maina, a trader at the market, said.

A nurse at the Biu General Hospital confirmed the number of dead.

No claim of responsibility was immediately made, but the Islamist militant group Boko Haram has terrorized northern Nigeria regularly since 2009, attacking police, schools, churches and civilians, as well as bombing government buildings.

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