MAIDUGURI, Nigeria -- A female suicide bomber pretending to wait in line for food handouts detonated her explosives Saturday, killing at least 13 people at a crowded market in northeastern Nigeria, authorities said.

A second female bomber killed herself and wounded many others, according to witnesses in the town of Biu, about 185 kilometers, or 115 miles, from the Borno state capital, Maiduguri.

"The first bomber pretended to be on the queue as one of the beneficiaries waiting for her turn to receive food," said Mohammed Maliya, who was part of the rescue effort. "She was so relaxed and was even eating a banana before she detonated."

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The incident came less than two weeks after more than 50 people were killed in a suicide bombing at a mosque in Mubi, 170 kilometers, or 105 miles, east of Biu.

While there was no claim of responsibility for Saturday's attack, suspicion immediately fell on the Boko Haram Islamic extremist group. Boko Haram has increasingly used women and children, often kidnapped and indoctrinated, to carry out suicide bombings.

Boko Haram has been blamed for more than 20,000 deaths in its eight-year insurgency, which has spilled over into neighboring countries and created a vast humanitarian crisis with millions displaced and hungry.