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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.

The Islamist group has said its aim is to impose a stricter form of Sharia, or Islamic law, across Nigeria, which is split between a majority Muslim north and a mostly Christian south.

Boko Haram has recently increased its attacks against troops and civilians in a country preparing for a March 28 presidential election. The group also has launched attacks in neighboring Cameroon and Chad.

Earlier this month, several African nations – including Nigeria, Niger, Benin, Cameroon, and Chad – pledged to deploy 8,700 troops, police and civilians as part of a regional effort to fight Boko Haram.

Thursday’s blast targeted the provision goods section of the market, which attracts shoppers from the town and neighboring villages.

“I was in my shop, attendi‎ng to customers, when I heard a loud explosion that made me duck under the table,” said Abacha Kachalla, another trader.

CNN’s Jason Hanna contributed to this report.