Islamist terrorist group Boko Haram has abducted thousands of children in the past five years.
They are forced to become fighters, sex slaves and porters.
Now the insurgents have embarked on a callous strategy. They are coercing girls into becoming suicide bombers.
A young woman walks toward a stadium where President Goodluck Jonathan is holding an election campaign rally.
She is dressed in the traditional Muslim garb and veil. Explosives are strapped tightly to her body.
The explosion detonates minutes after the head of state left the venue in Nigeria's north-eastern city of Gombe, the capital of Gombe State.
It kills one person and injures 18 others.
A few hundred kilometres further north, two child suicide bombers kill four people in a crowded market in Potiskum, a small town in Yobe State.
In neighbouring Borno State, a ten-year-old girl sets off a bomb at a market in Maiduguri, killing at least 19 people.
As security in northern cities gets tighter in the run-up to Nigeria's February 14 general election, Islamist terrorist group Boko Haram has come up with a new strategy to smuggle bombs into highly populated areas.
It increasingly uses young women and girls, relying on the fact that they are not body-searched by male security officers and rarely suspected to be terrorists.
“Adult suicide bombers are more easily identified than children. Especially young girls wearing a Muslim veil will not be suspected or searched,” says Hussaini Abdu, Nigeria director of international charity ActionAid, which assists Boko Haram victims.
“Children can easily be indoctrinated or coerced, especially in a religious and patriarchal environment,” he says.
Abdu suspects that many girls are sent on suicide missions against their will, with the bombs being remotely detonated.
UN Secretary-General Ban Ki-moon condemned Boko Haram's use of child suicide bombers as a “depraved act.”
“The perpetrators of these attacks show no signs of stopping as they increasingly target innocent children,” United Nations children's fund UNICEF executive director Anthony Lake has warned.
Thousands of children had been traumatised by Boko Haram, Lake said.
Boko Haram kidnapped 276 school girls from their dormitory in the town of Chibok in north-eastern Borno State in May, prompting an outcry. Fifty-three later managed to escape.
But it wasn't the first time the insurgents kidnapped children to use them for their purposes, nor was it the last.
“The Chibok kidnapping was no isolated incident. It was just the biggest,” explains Bukola Shonibare, leader of the Bring Back Our Girls campaign, which was launched to lobby for an intensified search of the missing children.
“There have been hundreds of abductions before Chibok, and hundreds since,” says Shoniboare.
Like other activists and researchers, she suspects some of the girls kidnapped in Chibok could have been forced to become suicide bombers.
“We think it's very likely,” says Shonibare. “We don't have proof, but we have received information from some of the escaped girls that point in this direction, as well as from people in villages near Boko Haram hideouts.”
Research group Human Rights Watch (HRW), which interviewed girls and young women who managed to flee terrorist camps, found that Boko Haram threatens victims with abuse, violence or death unless they convert to Islam, stop attending school or commit crimes.
Victims told the researchers how they were used for tactical reasons, for example to lure security forces into an ambush, force payment of a ransom or for a prisoner exchange.
“I was told to approach a group of five men we saw in a nearby village and lure them to where the insurgents were hiding . When they followed me for a short distance, the insurgents swooped on them. 1/8They 3/8 slit the throats of four of them . Then I was handed a knife to kill the last man. I was shaking with horror and couldn't do it,” one escapee told HRW.
But most abducted children are not lucky enough to find a way to run away. Almost ten months after the abduction of the Chibok girls, there is still no trace of the majority of them.
The Bring Back Our Girls campaigners continue to meet daily at the Unity Fountain in central Abuja to protest the kidnapping and the government's failure to rescue the children.
“The silence around the girls' fate is deafening,” says Shonibare.
“We don't have any information right now that provides us with hope. The families are completely traumatised.”
Some parents find it hard to believe that some of the girls might have been forced to carry out suicide bombings, the campaign leader said.
“The least government could do is to heighten security to prevent the abduction of more and more children,” says Shonibare.
“They finally need to take responsibility.”