When Boko Haram fighters kidnapped 17-year-old Nadia and took her to their camp, their commander noticed her straight away. She was squatting with dozens of other abducted women in front of him, listening to his lecture.

When, a few minutes later, the commander ordered his men to take Nadia to his house, she asked: “Why only me?” But she went with the men and waited.

The commander, whose name she never learned, “was dirty, ugly, dark-skinned and had a beard. He had a lot of hair on his head like a madman,” Nadia remembered. He looked mean. And he wanted her as a second wife.

Three months later, Nadia woke up one morning to find her body strapped with explosives. She had been drugged the night before. The commander’s men pushed her on to a motorbike, and dropped her and two others near Gamboro, a town in Borno, the Nigerian state hit worst by the Boko Haram insurgency.

The mission they had been given: to blow themselves up in as big a crowd as they could find.

They gather all the women and preach and preach. Then they ask: ‘Who wants to go to paradise?’ Aisha

Boko Haram, the terrorist group best known for kidnapping hundreds of schoolgirls from the village of Chibok in the middle of the night three years ago, has been under heavy attack from the Nigerian military in recent months.

But as their longed-for “caliphate” across north-eastern Nigeria has shrunk, the number of bomb attacks has increased, with the insurgents increasingly sending the women and children they have abducted to blow themselves up.

The week before Nadia was abducted, Boko Haram had attacked her village. Hiding behind her house, she had listened as they searched for her father, screamed at her mother for trying to hide him, and finally found and shot him.

When the commander announced to Nadia that he was making her his concubine, she was told she was one of the “lucky few” to be selected. But terrified as she was, Nadia had no intention of going along with it.

“He came that night and tried to rape me,” she said, her diamante earrings glinting through her pale blue hijab. “We wrestled seriously. I thought, this is a life-or-death situation, he probably has an STD which would kill me anyway, so I might as well die honourably. I used all my strength to fight him, and he was so angry when he couldn’t succeed in raping me. In the morning he went out and called his boys, and told them to take me out and flog me.”

After more death threats and another rape attempt, he tried a different tack: talking to her, trying to persuade her to accept the marriage. But after three months of cajoling, he had had enough, and decided to get rid of her.

That was how Nadia found herself approaching a checkpoint run by the civilian joint taskforce (CJTF), a paramilitary group helping fight Boko Haram in north-eastern Nigeria, trying to keep her arms out from her sides and not to swing them, to avoid accidentally detonating the bomb strapped to her waist.

When the men at the checkpoint saw the three women approaching, they shouted at them to stop. The women had prepared for this moment – in the minutes after their captors had left them, they had agreed to try to hand themselves in.

In this 2015 photograph civilians walk past a checkpoint manned by Nigerian soldiers in Gwoza, a town newly liberated from Boko Haram. Photograph: Lekan Oyekanmi/AP

“We stopped. We shouted: ‘We’re carrying bombs, we were forced to,’ and we lifted up our veils and showed them the belts,” she said.

They were fortunate: no gun was raised to shoot them. The men called the military and after a 40-minute wait, standing still under a tree, soldiers came and removed the bombs from their bodies.

“I was so happy; we were smiling and laughing,” Nadia said. “We had survived.”

Many do not survive: according to figures collated by the Long War Journal, 154 bombers have died in Nigeria, Cameroon, Niger and Chad since 2014, and this is a conservative estimate, as many attacks go unreported in the media.

When preparing someone for a “suicide” mission, Boko Haram members treat the bomber as if they are already dead, preparing the body as if for their own funeral.

“What they normally do is to dress you very beautifully, and put henna on your hands,” said Aisha, who was “married” to Boko Haram’s fourth-in-command and recently escaped. She saw many women and children recruited and sent on such missions.

This happened to Fatima, now 20, before she was sent to blow herself up in 2015. “They tie your hair back to prepare you for death,” she said, her voice quiet as she removed her red headscarf to show how her hair was braided off her face, as is the custom in funeral rites.

Fatima was raped every night by several different men for eight months, and is still terrified that somehow Boko Haram will find her and kidnap her again. By the time she was chosen for a bombing mission, she was so frightened that she could not speak, and stayed silent throughout the preparations.

“I was so afraid. I didn’t know what they meant. I’d never heard of anyone blowing themselves up. They told us we should go into a crowd and hit here,” she said, touching her hip. “Nobody told us what [the vest] was, but I knew it wasn’t something good. I didn’t look at it.”

She was dropped near Kukara, the target her captors had chosen for her, but she never considered going through with what she had been instructed to do.

“I went up to some soldiers and said: ‘I’m carrying something round my waist,’” she said. “They raised my veil and when they saw it they all jumped back. One said: ‘It’s a bomb!’ I was terrified, I was crying, but they told me not to move.”

Like Nadia, Fatima was believed by the soldiers. The bomb was removed, she was put through a rehabilitation process for three months, and is now living with her mother and sister. However, fearful of the heavy stigma that comes with having lived under Boko Haram, she has told them a sanitised version of her experiences during the abduction. (The names of all the women in this article have been changed.)

Nadia and Fatima were sent on their aborted missions in 2015. At that time, Boko Haram tried to hide the fact they were forcing people to blow themselves up from their other prisoners, afraid they would attempt to run away, according to Aisha, who observed how things changed over her three years in captivity. Now, she said, they have become completely open about it.

“They preach that if you go to [the state capital] Maiduguri and kill people, you will go to paradise without question,” she said. “They have a lot of ways to persuade them. They say: ‘Don’t consider them Muslim brothers and sisters any more – just go and kill them.’

“They gather all the women in one area and preach and preach. Then they ask: ‘Who wants to go to paradise?’ Everyone raises her hand. Then they ask: ‘Who wants to go now?’ Some raise their hands, so they take them and train them in suicide bombing. If nobody raises her hand, they say: ‘God created you, fed you, did everything for you, and this is how you reward him for all this?’ They make sure they get at least one person.

“It doesn’t take long to train them. They either tell you to hold the bomb or they strap it on to your body, round your waist or inside your bra. They tell you to go anywhere where there are a lot of men. They say: ‘Pretend you have stomach pain and fall on the ground. When people gather round you, press the button.’

Aisha saw how they recruited children as young as five for the missions.

“They say: ‘Who wants to go and see their mother in paradise? If you want to see her, that’s where she is.’ The children accept it easily, because they don’t know how dangerous it is. They tell them they won’t feel any pain even if their body is destroyed. I heard them saying that to the children in my camp.”

More and more children are being used in such missions: according to figures collected by Unicef, 27 were killed while wearing bombs in north-eastern Nigeria in the first three months of 2017, a sharp rise from 2016, when 30 were killed in the whole year.

It is the job of Bamussa Bashir, chair of a Maiduguri branch of the CJTF, to ensure that some of his 102 members are always guarding their area of the city, looking out for strangers who could be Boko Haram members or bombers. Women, and especially young girls, are increasingly being regarded with suspicion in Maiduguri.

In February Bashir, a quiet, serious-looking 23-year-old, was in a Maiduguri market, full of people buying beancake and grilled meat, when two girls got out of a car. A young man he didn’t know, buying credit for his phone, said to Bashir: “I don’t trust those girls.”

One of the girls hailed a tuk-tuk and zoomed off. The other started walking towards the market stalls. Bashir jumped up, wondering what to do, and was amazed to see the young man he had just been talking to head straight for the girl and put his arms around her.

“He grabbed her, trying to drag her away from the crowd. Then the bomb exploded.” As well as the young man and the girl, seven others died in the explosion, but the death toll could have been higher.

The hugging technique – when someone grabs a suspected attacker and uses their own body as a shield so fewer people around them die – is one of the only things locals can think to do in the face of the bomb attacks.

“People started doing it in one area, then another – it spread,” said Bashir, adding that he was ready to do it himself if it meant risking his life to reduce casualties.

“I know what death means. I’ve seen my relatives die and they have not come back. My brother was killed by Boko Haram two years ago. That’s part of the reason I do what I do, but what I really want is peace.”