Four suicide bombers have killed 19 people in a series of attacks that targeted a civilian self-defence force and the people who gathered to mourn their deaths, police in Nigeria said, according to The Independent.

It is the latest in a spate of suicide bomb attacks on the city in the last few weeks. Borno, of which Maiduguri is the capital, is the Nigerian state worst affected by the eight-year-old insurgency by Islamist militant group Boko Haram.

Borno state police commissioner Damian Chukwu said 23 others were wounded in Tuesday night's attacks.

The police commissioner said 12 of the dead were members of the civilian self-defence force and the other seven people had been mourning them.

At least one of the suicide bombers was female, said a spokesman for the self-defence force, Danbatta Bello.

The bombers specifically targeted his colleagues while they were on duty, he said.

“A teenage female suicide bomber actually crept to the sandbag post of our boys at Molai and before they could realise what was happening she detonated herself and killed three of our boys,” Mr Bello said.

“That happened simultaneously with the one that occurred at the tea vendor's, where seven of our members who took their time off to eat their dinner were killed.”

Boko Haram has increasingly used girls and young women to carry out attacks on marketplaces, checkpoints and other targets.

Some young women who escaped extremist group have said girls are drugged and forced to carry out suicide missions.

Nigeria's government declared late last year that Boko Haram had been “crushed” but deadly attacks continue.