Two female Boko Haram (WTF is Boko Haram?) suicide bombers blew themselves up Tuesday morning at a refugee camp in Northeastern Nigeria, killing at least 58 people, CNN reports.

Some of the refugees targeted in the attack were former Boko Haram sex slaves, whom African troops freed last week.

On Tuesday, a third woman was supposed to blow herself up, but she realized at the last minute that her parents and siblings were living in the camp. Another two would-be bombers failed to set off their explosives.

A total of 78 people were injured in the attack. The twin suicide bombing occurred in the town Dikwa near Nigeria’s border with Cameroon.

The bombings were said to be retaliation for a recent military offensive in the area. Troops raided three Boko Haram strongholds last week, killing more than 100 militants and freeing more than 1,000 people. Those freed included more than 100 female sex slaves.

Boko Haram has killed about 20,000 people in its 6-year Islamic insurgency. The terror group has also displaced more than 2 million people.