At least eight people are dead after female suicide bombers attacked two displaced persons camps in northeastern Nigeria's main city, a civilian self-defense group said Monday. 

It was the first major attack on a displaced persons camp in Maiduguri, the birthplace of the Boko Haram extremist insurgency.

The attack started late Sunday night and left another 15 people wounded, spokesman Bello Danbatta with the Civilian-JTF group told The Associated Press.

The Nigeria-based extremist group Boko Haram often targets the city with suicide bombers and increasingly has been using female ones. 

Nigeria's government late last year declared the group "crushed" but dozens of such attacks have been carried out this year.

The latest bombings occurred a few days after Nigeria's army chief of staff issued a 40-day deadline for troops to flush out Boko Haram's leader and finish off the extremist group.

Danbatta said one bomber sneaked into the Dalori camp and detonated, and two other attackers exploded on or near the camp's perimeter fence. 

Another bomber detonated early Monday morning.

Thousands of people continue to shelter in camps after being forced from their homes by Boko Haram. 

The extremist group's eight-year insurgency has killed more than 20,000 people, kidnapped thousands of others, spilled into neighboring countries and created one of the world's largest humanitarian crises.

Nigeria is moving closer to famine, with more than 5 million people expected to face "crisis, emergency and famine conditions" by the end of August as the lean season continues, the Norwegian Refugee Council said in a statement Monday. The unrest has disrupted farming and access to markets in the region.

Threats to displaced person's camps have included Nigeria's own military. On Monday, the air force issued a statement expressing its "deepest regrets" for mistakenly bombing a camp in the town of Rann in January. 

A Borno state government official said more than 230 people were killed when the air force bombed the camp multiple times. Last week the military said the camp was not appropriately marked as a humanitarian base on its operational maps.

AP