Millions of men, women and children around the world are currently victims of human trafficking - bought and sold as commodities into prostitution and forced labour.

This trade in people criss-crosses the globe - and it is a lucrative business. The International Labour Office estimates that forced labour generates $150bn (£96bn) in illegal profits every year. Two thirds ($99bn; £63bn) comes from sexual exploitation.

But who are the people behind the numbers?

Kemi and Bilkisu, from Nigeria, Jane from the UK and Gabby from the US describe how they fell prey to traffickers.

Kemi's story, Nigeria

Thousands of women and girls from West Africa are bought and sold every year - most end up in Europe. The UN's Office on Drugs and Crime estimates West African trafficking victims, many of whom originate in Nigeria, make up about 10% of those forced into sex work in Western Europe.

Benin City, in Nigeria's south, is a key player - with networks and infrastructure built around the trade in people.

Image caption Benin City, in Nigeria's south, is a known trafficking hub

There, traffickers scout for girls wanting to travel, enticing them with promises of work and education. The victims are offered false papers and told they will need to pay off the cost of their transit when they reach their destination country.

Once recruited, the girls are often forced to take part in rituals to ensure their compliance.

One female former trafficker in Benin City describes how traffickers take girls' clothes as well as hair from their head, armpit and pubic area and hand them over to a traditional preacher in a ceremony, as a pledge that they will pay back their debts.

"With all those things collected from them, they have this fear that anything can happen," she says.

Media playback is unsupported on your device Media caption A Nigerian trafficker explains how she supplies women for a profit and the risks involved.

One of those who fell victim to the lies of the traffickers is Kemi. She was promised a new life in Italy - one that would allow her to provide for her family.

"They said, 'We want to change your life. We just want you to be happy'," she tells the BBC.

Image caption Kemi was tricked into work in the sex industry

On her arrival in Italy, Kemi, a Catholic, soon learnt that the reality of her new life was far from what was promised.

She [the trafficker] is sending her children to the best schools with the money that I earned with my body Kemi, Nigerian trafficking victim

She was told she would be expected to work as a prostitute. Although she initially refused, after being denied food and having her phone taken from her as punishment, she began to do as she was told.

"In the end, I worked for three years and three months," she says.

Over that time, Kemi paid a total of €27,000 ($30,000; £19,000) to her traffickers - an amount they were still not satisfied with.

She eventually found the strength to leave their clutches and escaped to stay with friends. However, she was deported by Italian authorities back to Nigeria some time later.

Without anything to show for her time spent abroad, Kemi decided not to return to her family.

"I was ashamed to go back home," she says tearfully. "I was ashamed to go back with nothing."

Now, traumatised by her experiences, she feels nothing but anger towards her traffickers.

"They are wicked," she says. "The woman that sent me has two girls. She is sending them to the best schools with the money that I earned with my body."

Bilkisu and Jane's story, UK

Hundreds of those trafficked from Nigeria end up in the UK, where they often face similar sexual exploitation or a life of forced domestic servitude.

Some 244 of the 2,340 potential victims referred to UK authorities in 2014 were from Nigeria, according to the National Crime Agency, a 31% increase on the previous year. The only country with a higher number of potential victims was Albania.

Bilkisu is one of those sent from Nigeria to the UK under false pretences. From the age of 15 she was kept as a slave - working long hours for no pay for almost 10 years.

Promised a place to stay with her uncle and the chance to continue her education, as well as provide her family with extra income, she left her homeland hoping for a better life.

However, once she reached the UK, she found herself being forced to do housework and childcare for her uncle's family. She began her chores at 05:00 and didn't finish until 21:00.

I was lonely... You know when you're inside a hole and there is no light - it is black. Everywhere was black Bilkisu, who was trafficked from Nigeria to the UK BBC

"Get the children ready for school, shower them, give them breakfast, iron the clothes," she says when describing her daily routine. "And also my auntie and my uncle, I had to get their clothes ready as well, as they needed to go to work."

During the day, Bilkisu cleaned the three-bedroom flat from top to bottom. If her aunt was not satisfied with the work done, she would be beaten.

"I was lonely... You know when you're inside a hole and there is no light - it is black. Everywhere was black. I was like that."

That damage is still there and, I don't know, it's going to be there forever and ever Bilkisu, Nigerian trafficking victim

In the nine years Bilkisu worked for her uncle and his family, she didn't have a single day off and never received any pay.

It was only when she reached her 20s that she began a series of desperate attempts to get help. She eventually escaped with the help of the pastor at her local church.

But, having been robbed of a childhood, she still finds it difficult to socialise.

"I don't know how to make friends anymore," she explains. "That damage is still there and, I don't know, it's going to be there forever and ever."

'Passed around UK'

Unlike Bilkisu, many child victims of trafficking in the UK are actually bought and sold within the country. The UK government believes there are currently 13,000 children being exploited in this way.

Jane was just 13 when she was groomed and then abused, before being trafficked across the UK by groups of men for sex.

It began while she was at school. A man in his 70s, who knew she had an unstable family life, began to offer her presents and lifts.

He was soon asking for repayment in sexual acts and, slowly, over time, he began passing Jane around other Asian men.

They burnt my hair, they've broken bits of my face. They've tried to douse me in petrol and set me on fire Jane, who was trafficked across the UK BBC

At first, the men would drive her around, offer her drugs and take inappropriate pictures of her, she says. But the abuse soon escalated.

"Within a few weeks the older male would lock the door with the men inside and they wanted sex. And they took videos, they took pictures, they'd given me things [drugs] to take."

Soon, Jane was being swapped between different groups of men across the country - sometimes hours away. They would meet at petrol stations to pass her between vehicles.

If she tried to object, the men would become violent and threaten her family.

I think because it started at an early age, after a while you just believe that that's all you're worth Jane, Groomed and trafficked in UK

"They'd throw you out of the car. They burnt my hair, they've broken bits of my face. They've tried to douse me in petrol and set me on fire," she says.

Because Jane's self-esteem was so eroded, she describes how she no longer put up a fight. She has been left with a number of injuries to her skull and nose as well as permanent internal damage.

"I was scared of what was happening. I think because it started at an early age, after a while you just believe that that's all you're worth."

Media playback is unsupported on your device Media caption The Salvation Army's Anne Read says modern slavery is more widespread than many people suspect.

Jane's abuse went on for nine years - sometimes every day, sometimes with months in between.

Her ordeal was made worse, she says, because police and other agencies didn't believe she was the victim. She finally escaped the clutches of the gangs by contacting the Salvation Army.

"I didn't really have to say much, they just understood and said, 'It's not your fault, we can help you'. Within two hours there was a car to pick me up to take me to a safe place."

Gabby's story, US

It is a similar story in the United States, where tens of thousands of children are being trafficked into prostitution. The Federal Bureau of Investigation (FBI) says child exploitation is at "near-epidemic levels".

Gabby, from Baltimore, says she was abused by her father between the ages of eight and 12 - a relationship that she feels has influenced how she interacts with men.

Image caption Gabby was abused by her father and turned to drugs

"I learnt very early that you could get things that you wanted or needed through sexual favours," she says.

Gabby says she turned to drugs and fell into a relationship with an addict who, years later, pushed her into prostitution.

I didn't have a choice either, but the crazy thing was I thought I did. Gabby, Forced into prostitution by boyfriend

"I didn't hesitate because I felt like he had taken care of me for all that time and I trusted him. I think that it was his plan to get me to trust him beyond any shadow of any doubt."

Gabby says she soon discovered the "boyfriend pimp" was nothing out of the ordinary on the streets, where she saw underage girls experimenting with drugs before being "snatched up by these guys and forced out there".

"The pimp would sit in his car on a certain corner wherever he had her working so that she would know that he wasn't far away. She was too afraid to run, you know, and there were about five girls out there like that when I was out there."

Media playback is unsupported on your device Media caption The FBI's Joseph Campbell says child exploitation in the US has reached near-epidemic levels

Gabby managed to escape the streets and leave her boyfriend and, with therapy, is starting to try to make sense of what happened to her. But she says for many of the young girls out on the streets - confused, terrified and trapped in those relationships - getting out can be a matter of life or death.

"And a lot of times you'll wind up going from one situation like that to another and not even realising the pattern of it, until you're able to get around somebody who can help you."

If you or someone you know has been affected by trafficking:

In Nigeria contact the National Agency for the Prohibition of Trafficking in Persons (NAPTIP) on 07030000203, 0800CALLNAPTIP (08002255627847) toll free

contact the National Agency for the Prohibition of Trafficking in Persons (NAPTIP) on 07030000203, 0800CALLNAPTIP (08002255627847) toll free In the UK call the modern slavery helpline on 0800 0121 700 run by the Home Office, but if you or someone else is in danger, call the police on 999

call the modern slavery helpline on 0800 0121 700 run by the Home Office, but if you or someone else is in danger, call the police on 999 In the US contact the National Human Trafficking Resource Center on 1-888-3737-888. In an emergency contact law enforcement on 911.

Series producer: Jacky Martens; Nigeria production by Sam Piranty; UK production by Jacky Martens; US production by Lindle Markwell, Sarah Svoboda and Sam Piranty

Web production by Lucy Rodgers, Dominic Bailey and Gerry Fletcher