Mamadou Yallow was out at school when police came for his family. Aged just 16, he returned to their home in Gambia to find his father and brothers had been arrested for involvement in an attempted coup against President Yahya Jammeh.

“The soldiers are looking for you, if they see you they’ll kill you,” he was told. So he ran.

But the journey Mamadou hoped would lead him to safety instead turned into a year-and-a-half-long nightmare of torture, imprisonment, war and death.

By the time the teenager was crammed into an overcrowded dinghy across the Mediterranean, he had already seen three of his friends beaten to death, watched women and children be raped, and been beaten, starved and sold as a slave.

Mamadou’s father, a soldier, was part of a failed coup against Yaha Jammeh (Getty)

Speaking to The Independent from Brussels, the 19-year-old described how he fled his home country in December 2014 following his father’s role in a failed coup against the country’s “dictator” of 22 years.

“They came and arrested everybody in my family while I was at school,” he said.

“There was nothing to do so I escaped to Senegal. I knew if I went back they would kill me and nobody would care.”

Mamadou joined friends making their way along a well-trodden migration route towards northern Africa and Europe via Mali.

But the teenagers had little knowledge of what was ahead and were driven by smugglers straight into the lawless “Azawad” region, where the Malian government, separatist rebels and al-Qaeda and Isis affiliates are battling for control.

Mamadou was kidnapped in the northern Malian region of Azawad (Getty)

After driving through the former Islamist stronghold of Gao, armed rebels stopped the lorry carrying Mamadou and around 100 other migrants and kidnapped everyone inside.

The teenager said militants attempted to force the refugees, including women and children, to join their ranks, beating them when they refused.

“They told us to make a long line and to jump, jump like a monkey dance,” he recalled. “They took our water, they took our money, they took everything that belonged to us.”

Mamadou was held by the militia for a week, seeing some of his friends beaten to death as the rest struggled to survive in soaring temperatures with little food or water.

Refugee crisis - in pictures Show all 27 1 /27 Refugee crisis - in pictures Refugee crisis - in pictures A child looks through the fence at the Moria detention camp for migrants and refugees at the island of Lesbos on May 24, 2016. AFP/Getty Images Refugee crisis - in pictures Ahmad Zarour, 32, from Syria, reacts after his rescue by MOAS (Migrant Offshore Aid Station) while attempting to reach the Greek island of Agathonisi, Dodecanese, southeastern Agean Sea Refugee crisis - in pictures Syrian migrants holding life vests gather onto a pebble beach in the Yesil liman district of Canakkale, northwestern Turkey, after being stopped by Turkish police in their attempt to reach the Greek island of Lesbos on 29 January 2016. 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He recalled how fighters would torment their captives by parading in front of them with bottled water, telling them to open their mouths before throwing it on the ground and laughing.

“They said we would die there,” he said. “They were raping the women in front of us, children, they don’t care.”

Prepared to risk their lives to escape, Mamadou and a friend made a break for freedom after telling guards they were going outside to urinate, running into the desert.

Fearing detection in the next village they found, they jumped on a lorry that drove over the border into Algeria.

The pair eventually found themselves in Ouargla – a common transit point for migrants attempting to reach Europe – and did weeks of hard labour to fund their onward journey.

But on the night of November 23 2015, a huge explosion ripped through the camp they shared with more than 650 migrants after an electrical fire set a stockpile of gas cannisters alight.

At least 18 people including two children were killed and many more injured, but Mamadou said he was lucky to be sleeping on the other side of the building.

The disaster garnered international news coverage and the attention of Algerian authorities, who ordered all migrants like Mamadou who had no visa or documentation to get themselves out of the country or be forcibly deported.

Weeks of hard labour in Algeria’s Ouargla region culminated in a deadly camp explosion (Getty)

So the teenager moved again, this time to Libya – where lawlessness reigns in swathes of the country still embroiled in civil war following the British-backed ousting of Muammar Gaddafi.

“We met an Arab man with a soldier’s uniform, he said he could help us and we would be safe,” Mamadou said. But his relief was shortlived – the man crammed him and six other migrants into a car and drove them to a large compound.

A man appeared and handed over a wad of cash to the driver, telling Mamadou: “I’ve bought you so you are all my slaves now.”

They were forced to farm and carry out hard labour but the teenager fell sick and was unable to stand, suffering from scabies and malnutrition. Mamadou’s friends were threatened with a gun to carry on working until one day they could not carry on.

“Three of my friends say they cannot do the work any more,” he recalled. “The man said: ‘I paid for you so I will kill you’.

“He killed them, beating them on the head. He told us to bury them or we would join them. We buried them in the garden.”

Desperate journeys: Rescued at sea, refugees detail abuse in Libya

Eventually Mamadou and three remaining prisoners managed to climb over a fence to freedom while their captor was out, finding other African migrants who gave them food, medicine and a place to stay.

But they had to once again risk searching for work, being caught by a gang of “Asma Boys” – notorious young armed robbers – who locked them up for ransom.

With no family to call to pay the money demanded in exchange for freedom, they were beaten every day until the gang gave up and handed them over to another group for forced labour.

After months of being shunted from one nightmare into the next, Mamadou was eventually able to find a smuggler who put him on an overcrowded dinghy from Sabratha into the Mediterranean.

The sea crossing is the deadliest in the world and the journey posed further trials as spilled fuel mixed with seawater leaking into the boat to create a burning, toxic chemical.

But Mamadou’s boat was rescued by a Spanish ship and taken to Sicily, where he was treated by Italy’s Medici per i Diritti Umani (MEDU) organisation for both his physical and mental wounds.

Months after his arrival in Europe, the teenager is far from recovered and broke down while speaking to The Independent about his experience.

An aid worker said he cannot stop returning to the memory of burying his dead friends, adding: “He’s still there. We hope soon he finds peace.”

African immigrants in Tripoli after being detained by the Libyan coastguard (Reuters)

Mamadou’s horrific story is just one of more than 1,000 testimonies gathered in a joint project by MEDU, the Hotline for Refugees and Migrants, Physicians for Human Rights-Israel and the Open Society European Policy Institute.

Their experiences, compiled into an interactive migration map of African migrants’ journeys to Italy, shows the terrible scale of torture experienced by those seeking safety.

The research found less than one asylum seeker out of 10 said they left their home countries for economic reasons, while more than 90 per cent were victims of extreme violence, torture or inhuman and degrading treatment.

Libya was the nucleus of kidnapping, detention and enslavement reported by the vast majority of refugees arriving in Italy, with nine out of ten migrants saying they had seen someone killed, tortured or severely beaten.

The country remains divided between a fragile government, Isis and more than 1,700 separate armed groups all implicated in the “industry of exploitation” while battling for control.

A migrants dingy boat pulled towards an aid ship during a rescue operation offshore of the western Libyan town of Sabratha (Getty)

It has become the main point of departure for almost 175,000 migrants who have arrived in Italy this year, mainly from Nigeria, Eritrea, Sudan and Gambia.

Another 172,000 have arrived in Greece, predomainantly from Syria, Afghanistan and Iraq, but the shorter and safer route over the Aegean Sea has been virtually closed by the EU-Turkey deal.

MEDU warned that migrants who have suffered trauma are at risk of developing severe mental disorders, making them chronically ill and also making it difficult to integrate in Europe or cope with the challenges posed in an increasingly hostile continent.

More than 80 per cent of refugees treated in the charity’s centres in Italy have physical wounds; many more suffer from PTSD, trauma, depression, anxiety and other mental illnesses that are often undiagnosed and untreated by authorities.

Alberto Barbieri, the group’s general coordinator, said the “hidden epidemic” must be addressed by Italy and other European nations.