Story highlights

The camp in northeastern Nigeria was set up as a refuge for people who had been victimized by Boko Haram

Sources say three female bombers, disguised as displaced people, entered the camp

Two set off their suicide vests; a third refused after learning family members were there

Kano, Nigeria CNN  — 

Two female suicide bombers between the ages of 17 and 20 blew themselves up this week in a camp in northeastern Nigeria set up to shelter people from terrorism, killing at least 58 people. But others were spared when a third intended bomber realized at the last minute that her family had taken shelter there, too, and refused to detonate her explosives, relief officials said.

Officials said 78 people were injured. The victims were staying in a camp for people who had been displaced by Boko Haram violence in Nigeria’s Borno state.

“There were three female bombers who entered the camp around 6:30 a.m. disguised as displaced persons,” said Satomi Alhaji Ahmed, head of the Borno State Emergency Management Agency. “Two of them set off their explosives in the camp while the third refused after realizing her parents and siblings were in the camp.”

Two other would-be bombers were also in the group but failed to set off their explosives for unknown reasons, he added. They remain at large.

The bombers struck at the camp Tuesday, in the town of Dikwa, Ahmed said. Dikwa is near the border with Cameroon.

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More than 53,000 people fleeing Boko Haram attacks from six districts are sheltering under military protection.

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Warnings of more bombers on the way

The suspect was injured in the attack and is now in custody, Ahmed said. The woman confessed that she and the two bombers were sent by Boko Haram, and she warned that more bombers were on the way, he added.

“She told the military officers who interrogated her that they were among several women detailed by Boko Haram to attack the camp,” Ahmed said. “She warned more attacks were underway as the female bombers would sneak into the camp in different guises.”

The attacks are believed to be reprisals for a recent military offensive against Boko Haram in its strongholds along the border with Cameroon, a military source said.

Last week, troops raided three Boko Haram strongholds, killing more than 100 fighters and freeing more than 1,000 people – including more than 100 women kidnapped and used as sex slaves by the insurgents, the military source said on condition of anonymity.

The source said that the freed women were brought to the Dikwa camp and that Boko Haram terrorists “are pained by that, and hence their decision to send in suicide bombers in revenge.”

Some of the women in the group of suicide bombers are thought to have been taken from villages by Boko Haram in previous raids and indoctrinated, Ahmed said.

A growing legacy of terror and death

Boko Haram is a militant Islamic group working in Nigeria and the border areas of Chad and Cameroon; its purpose is to institute Sharia, or Islamic law. Boko Haram militants live primarily in the northern states of Nigeria, including Borno.

The group has provoked international condemnation with its brutality and mass kidnappings of women and girls.

On Saturday, militants from Boko Haram riding motorcycles at night killed 65 people in a raid.

CNN’s Forrest Brown contributed to this report from Atlanta.