Soldier, suicide bomber, executioner –- and child.

In the latest beheading videotaped by the terror group Boko Haram, one of the jihadis holding a gun on the victims looks very young. He’s not identified, and U.S. intelligence analysis of the video can’t pinpoint an age, but experts say it wouldn’t be shocking if he were a teenager. The Nigerian Islamists are increasingly relying on children – both male and female, and some as young as 10 -- to do their dirty, deadly work.

"There are enough reports to indicate there is a pattern," said J. Peter Pham, director of the Africa Center at the Atlantic Council, who says kids are smuggling weapons, spying on Nigerian military garrisons, executing local leaders in town squares and mounting armed attacks against civilians.

In January, Boko Haram released photos showing its training camp for child soldiers, and described the young boys as “Cubs of the Caliphate.” The images shows kids dressed in blue and black clothing and aiming automatic rifles. The photos were apparently the first released by the terror group showing child soldiers.

The terror group, which has been expanding its “caliphate,” has an increasing need for new soldiers. "As they seize more and more territory, you are seeing a lot more children being used," said a U.S. intelligence official. "It's their bench strength." She pointed to Boko Haram raids across the border in Cameroon, where villages have been emptied of males from 45 down to 10 years old. “You will now see fighters as young as 13,” she said.

A second U.S. intelligence official agreed that kidnapping of children is growing, stating that part of it is just Nigerian demographics. "When the bulk of your population is quite young, you have a child soldier problem," he said. As the demand for soldiers goes up, "there are more kidnappings.”

But not all the kids are unwilling recruits. Some, said the first official, join just to escape the grinding poverty of northeast Nigeria.

Many boys enter the service of Boko Haram as "Al Majiri boys," says Pham. It's common in Islamic Africa, he says, for poor families to send their young sons to study with imams, who also board the boys. The imams have the boys beg for money and food. Boko Haram recruits the boys, and then asks them to do their begging outside Nigerian military garrisons to conduct surveillance.

The children are also being used as killers, but they aren’t always carrying guns into battle. There are more and more instances of young boys used as executioners and spies, and in the most horrific example, of pre-adolescent girls being turned into suicide bombers.

So far, say U.S. officials, at least a half dozen girls, some as young as 10, have been sent into markets and other public spaces where they -- or Boko Haram militants operating remote control devices -- detonate the bombs.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

"We're starting to see remote detonation," said the first official. "The girls may not have known they were carrying a bomb. It's horrific."

There is also concern that some of the more than 300 girls who were kidnapped last April from a school in Chibok have been among the suicide bombers.

"Getting the girls? Extremely simple," a journalist in Maiduguri, the largest city in the northeast of Nigeria, recently told NBC News. The journalist not to be named because of restrictions imposed by his employer. "Many towns and villages have been raided, and married women, young girls and even children below 10 have been abducted. These are the suicide bombers."

Said a U.S. intelligence official, "It wasn't until the mass kidnapping of girls in Chibok that we saw the uptick in the number of suicide killings carried out by girls. That's what concerns us." So far, she said, the U.S. has seen around a half-dozen such bombings using young girls with the bodies too mutilated to be identified.

Throughout the northern part of the country, there are growing fears of more bombings. The intelligence official pointed to an incident over the weekend in the city of Bauchi in which a teen girl was beaten and burned to death after she was found to have two bottles tied to her waist.

Eyewitnesses told reporters that the girl refused to be screened with a metal detector at the entrance of Bauchi's crowded market. When the girl raised her veil, the crowd saw the bottles attached to her waist and, believing she was a suicide bomber, attacked. According to UPI, a mob then put a petrol-covered tire over the badly beaten girl's head and set her on fire. She was dead when police arrived.

The U.S. intelligence official noted that while there was no evidence the girl was on a mission and no explosive materials were found on her body, Nigerian officials believed she could have been on a dry run for a later attack. Markets and transportation terminals near the markets have been a favorite target of Boko Haram, she noted.

Another girl who was kidnapped in Chibok was apparently traveling with a Boko Haram assault team that attacked a village in her home region. According to Emmanuel Ogebee, a Nigerian-American human rights attorney, the girl’s job was carrying ammunition for the attackers.

Though her Boko Haram captors were standing next to her, said Ogebee, the girl asked the villagers if they recognized her and told them her real name. (Boko Haram has given the girls new Muslim names.) She spoke the local language to the villagers so her captors wouldn’t understand.

According to Pham, forcing the kids to attack their own villages and kill their old neighbors is meant to prevent them from deserting, in a technique he says is familiar from the Liberian civil war 20 years ago.

When Boko Haram wants to kill local officials or the local imam, he said, they have young recruits from nearby towns perform the executions in public.

"By doing this, it would seal in blood that the young recruits couldn’t go back,” said Pham. “They will be marked men in the area. That would prevent them from going back. From there, they graduate from executioner to fighter."

Teen boys also helped commit some of Boko Haram’s worst atrocities, like January’s massacre of as many as 2,000 people around the city of Baga on Lake Chad.

According to a U.S. counterterrorism official, militants went door-to-door killing families, then strategically placed improvised explosive devices in the streets to funnel survivors into areas where firing squads, many including teenagers, were pre-positioned. "They were mowed down" by automatic weapons fire, the official said.

The villages were then set on fire, and militants moved on to other areas to repeat the process, officials told the BBC. Those attacks also included a suicide bombing by a 10-year-old girl.

The use of girls as suicide bombers seems to have been adapted from the Taliban, which used boys.

“This is only one of several indicators that global jihadists are in a feeding off frenzy to outdo each other's atrocities,” said Ogebee.

Ogebee noted that in its first-ever Twitter post last month, Boko Haram released videos of child soldiers training. Weeks later, ISIS followed with a video of its own child soldiers training.

After the kidnapping of the Chibok schoolgirls in Nigeria, ISIS began abducting women as sex slaves.