“I told myself, ‘Look at yourself – you came to Europe, what was your aim?’ I am not doing this because I like it but I don’t have the money, I don’t have a choice.”

Those are the words of one of many refugee children forced into selling sex to survive in Greece, where a four-year-old girl is among those raped in camps that were supposed to afford them protection.

A study by Harvard University is warning of a “growing epidemic” of sexual exploitation and abuse in the country, which houses 62,000 asylum seekers stranded by the EU-Turkey deal and border closures through Europe.

“We had a case of a four-year-old girl who was raped,” a psychologist at a camp in Athens told researchers. “The mother did whatever was possible to report it.”

But aid workers and officials say there is often nowhere to turn, with victims trapped in camps with their abusers too frightened to go to police or authorities, who frequently lack interpreters and specialists.

The absence of arrests can lead asylum seekers to take violent retribution. In one Greek camp, a man who had already married one child raped another underage girl, and was badly beaten by other migrants.

Aid workers told the FXB Center for Health and Human Rights of criminal gangs “thriving” in squalid camps, where many refugees have been living for more than a year, and terrorising victims into silence.

Refugees in Greece: “Every day you die many times”

“Having endured the risks of sexual violence or having experienced sexual violence during their journey, migrant children suffer from the fear of sexual abuse in a place that should have guaranteed them safety and protection,” the report said.

It found that “weak or non-existent” structures leave children at heightened danger, with reports of sexual assault rising while gangs blackmail minors and threaten to send humiliating photos to their families.

“A man from one of the ‘mafia’ groups asked a couple’s seven-year-old daughter into their tent to play games on his phone and then zipped up the tent,” a doctor told researchers.

“She came back with marks on her arms and neck. Later, the girl described how she was sexually abused.”

Rape and sexual assault is feared to be significantly underreported because of the fear of retribution and stigma, while administrative backlogs can cause long delays before victims can be moved away from their abusers.

The EU-Turkey deal has left thousands of children detained among 13,000 migrants in overcrowded island camps, despite concerns from the UN over unsafe conditions seeing several refugees die of hypothermia and killed in fires over the winter.

Charities previously warned of rising self-harm and attempted suicide in detention centres and elsewhere in Greece, where at least one asylum seeker has killed himself this year amid rising desperation to escape.

Smugglers in Greece, Italy and elsewhere in Europe are known to force refugees including children into prostitution to pay “debts”, while migrants are also resorting to “survival sex” for food and shelter, or to raise money to leave Greece.

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. Getty Images Refugee crisis - in pictures Refugees flash the 'V for victory' sign during a demonstration as they block the Greek-Macedonian border Refugee crisis - in pictures Migrants have been braving sub zero temperatures as they cross the border from Macedonia into Serbia. Refugee crisis - in pictures A sinking boat is seen behind a Turkish gendarme off the coast of Canakkale's Bademli district on January 30, 2016. At least 33 migrants drowned on January 30 when their boat sank in the Aegean Sea while trying to cross from Turkey to Greece. Getty Images Refugee crisis - in pictures A general view of a shelter for migrants inside a hangar of the former Tempelhof airport in Berlin, Germany Refugee crisis - in pictures Refugees protest behind a fence against restrictions limiting passage at the Greek-Macedonian border, near Gevgelija. Since last week, Macedonia has restricted passage to northern Europe to only Syrians, Iraqis and Afghans who are considered war refugees. All other nationalities are deemed economic migrants and told to turn back. Macedonia has finished building a fence on its frontier with Greece becoming the latest country in Europe to build a border barrier aimed at checking the flow of refugees Refugee crisis - in pictures A father and his child wait after being caught by Turkish gendarme on 27 January 2016 at Canakkale's Kucukkuyu district Refugee crisis - in pictures Migrants make hand signals as they arrive into the southern Spanish port of Malaga on 27 January, 2016 after an inflatable boat carrying 55 Africans, seven of them women and six chidren, was rescued by the Spanish coast guard off the Spanish coast. Refugee crisis - in pictures A refugee holds two children as dozens arrive on an overcrowded boat on the Greek island of Lesbos Refugee crisis - in pictures A child, covered by emergency blankets, reacts as she arrives, with other refugees and migrants, on the Greek island of Lesbos, At least five migrants including three children, died after four boats sank between Turkey and Greece, as rescue workers searched the sea for dozens more, the Greek coastguard said Refugee crisis - in pictures Migrants wait under outside the Moria registration camp on the Lesbos. Over 400,000 people have landed on Greek islands from neighbouring Turkey since the beginning of the year Refugee crisis - in pictures The bodies of Christian refugees are buried separately from Muslim refugees at the Agios Panteleimonas cemetery in Mytilene, Lesbos Refugee crisis - in pictures Macedonian police officers control a crowd of refugees as they prepare to enter a camp after crossing the Greek border into Macedonia near Gevgelija Getty Images Refugee crisis - in pictures A refugee tries to force the entry to a camp as Macedonian police officers control a crowd after crossing the Greek border into Macedonia near Gevgelija Getty Images Refugee crisis - in pictures Refugees are seen aboard a Turkish fishing boat as they arrive on the Greek island of Lesbos after crossing a part of the Aegean Sea from the Turkish coast to Lesbos Reuters Refugee crisis - in pictures An elderly woman sings a lullaby to baby on a beach after arriving with other refugees on the Greek island of Lesbos after crossing the Aegean sea from Turkey Getty Images Refugee crisis - in pictures A man collapses as refugees make land from an overloaded rubber dinghy after crossing the Aegean see from Turkey, at the island of Lesbos EPA Refugee crisis - in pictures A girl reacts as refugees arrive by boat on the Greek island of Lesbos after crossing the Aegean sea from Turkey Getty Images Refugee crisis - in pictures Refugees make a show of hands as they queue after crossing the Greek border into Macedonia near Gevgelija Getty Images Refugee crisis - in pictures People help a wheelchair user board a train with others, heading towards Serbia, at the transit camp for refugees near the southern Macedonian town of Gevgelija AP Refugee crisis - in pictures Refugees board a train, after crossing the Greek-Macedonian border, near Gevgelija. Macedonia is a key transit country in the Balkans migration route into the EU, with thousands of asylum seekers - many of them from Syria, Afghanistan, Iraq and Somalia - entering the country every day Getty Images Refugee crisis - in pictures An aerial picture shows the "New Jungle" refugee camp where some 3,500 people live while they attempt to enter Britain, near the port of Calais, northern France Getty Images Refugee crisis - in pictures A Syrian girl reacts as she helped by a volunteer upon her arrival from Turkey on the Greek island of Lesbos, after having crossed the Aegean Sea EPA Refugee crisis - in pictures Refugees arrive by boat on the Greek island of Lesbos after crossing the Aegean sea from Turkey Getty Images Refugee crisis - in pictures Beds ready for use for migrants and refugees are prepared at a processing center on January 27, 2016 in Passau, Germany. The flow of migrants arriving in Passau has dropped to between 500 and 1,000 per day, down significantly from last November, when in the same region up to 6,000 migrants were arriving daily.

Eleni Kotsoni, a psychologist at a Médecins Sans Frontières (MSF) clinic in Athens, told The Independent that an increasing number of asylum seekers were coming forward about the phenomenon.

“It’s not something they talk about easily,” she said. “They are basically doing it to be safe, to be sheltered, to have a roof over their head, to have food in the winter.

“This can be children who are unaccompanied, or it can be women who come here without a husband or person to protect them.”

Refugee women can make “deals” with men from their home countries in exchange for safety inside detention camps, where overcrowding, outbreaks of violence and a lack of security and facilities leave them vulnerable.

In Athens, Thessaloniki and other cities, refugees tend to live in open camps or informal settlements, where adolescents may be preyed on by older men.

Children desperate to raise money or find shelter also seek to sell sex themselves, particularly in notorious parks in Athens where they wait to be approached by paedophiles.

The Harvard study found that the purchasers of migrant child sex were mainly men over 35, while children engaging in “survival sex” are mainly teenage boys, particularly from Afghanistan.

Some refugees have been trapped in Greek camps for more than a year (AP)

“Elderly men offer food and shelter to children,” an informant told researchers.

“They are willing to satisfy the children’s basic needs in exchange for sexual services, but the children want money.”

Some purchasers demand children to accompany them to their homes or meet at a hotel, the report said, while others insist on having sex in a park such as the notorious Pedion tou Areos (Field of Ares) in Athens.

The report found prices “rarely exceed €15 (£13) per exchange”. With smugglers hiking fees as borders and fences have gone up across Europe, prospects of escaping Greece are fading.

One child said he had “given up the hope of finding a way out of Greece, but other boys are still trying to collect the money to leave”, while another told journalists: “I never thought I’d have to do something like this.

“When the money ran out, I had to learn to do this…it was the first time I did this, I had no experience.”

Aid workers expect the situation to worsen as refugees remain trapped in Greece for ever-lengthening periods and relocation programmes including a British scheme are scrapped.

Within the first 10 months of 2016, more than 10,400 children applied for asylum in Greece, mostly from Syria, Afghanistan, Pakistan, Iran and other Middle Eastern and north African nations, creating huge backlogs in an unprepared system.

A migrant sleeps outside a tent in the port of Piraeus, where nearly 1,500 refugees and migrants live in a make-shift camp (AFP/Getty)

But by the end of the year only 2,413 migrant children – 11 per cent of those stranded in the country – had been successfully relocated to other European countries despite 160,000 slots being promised.

​Marleen Korthals Altes, a senior child protection adviser at Save the Children, said the closure of borders through the Balkans route had increased the risk of sexual violence and exploitation.

“People are remaining either in camps that are generally lacking security and law enforcement on the mainland…accommodation is poor and people are living in limbo,” she told The Independent.

“They came with a certain amount of money to survive but they got stuck and it has run out, and now they are desperate.”

Ms Korthals Altes said that although child protection is heavily legislated in Greece, laws are “inconsistently applied” by overwhelmed authorities, adding: “The policies and the practices are different.”

The Harvard report identified six major risk factors needing to be urgently addressed – the lack of children’s facilities, risky living conditions inside camps, unsupervised mixing of migrant adults and children, under-resourced child protection systems, a lack of coordination among authorities and a “radically inadequate” relocation scheme.

Its authors, Vasileia Digidiki and Jacqueline Bhabha, concluded that EU policies were exacerbating risks by forcing the youngest and most vulnerable refugees to turn to smugglers and take desperate measure to meet their extortionate fees.