Maiduguri, Nigeria – In a horrific turn of events, two girl suicide bombers killed at least three people and wounded 17 at a market in the northeastern Nigerian city of Maiduguri on Sunday, a spokesman for state emergency agency NEMA, Sani Datti, told Reuters.

The two young girls, approximately seven or eight years old, blew themselves up in the market on Sunday. Residents said about nine people had been killed.

Boko Haram hardliners have been waging an insurgency for seven years in the region to try to establish a self-proclaimed and ISIS-styled caliphate.

The extremists frequently target crowded areas – such as markets, places of worship and refugee camps – in suicide bomb attacks across northeast Nigeria and in neighboring Cameroon and Niger.

They have killed over 15,000 people and forced more than two million people to flee their homes.

In February 2015, Boko Haram used an eight-year-old to carry out a suicide attack in Potiskum, in Yobe state, and a 10- and 18-year-old pair were involved in a failed July 2014 attack in Funtua, in northwestern Katsina state.

Nigeria’s army has pushed the militant group back to its stronghold in the vast Sambisa forest in the past few months but the group still stages suicide bombings.