The ousted Libyan dictator Colonel Gaddafi kidnapped and raped hundreds of teenagers in specially built sex dungeons, according to a television documentary to be screened by the BBC next week.

Victims and witnesses state that Gaddafi would choose his targets on visits to schools or colleges, patting those on the head who caught his eye.

His security officials would then take the victim to one of several specially designed suites of rooms, one of which is located in Tripoli university, where they would be abused and raped by the dictator.

In the rooms at the university there is a fully equipped gynaecological suite, where victims would tested for STDs before being sexually abused.

"Some were only 14," recalled one teacher at a Tripoli school. "They would simply take the girl they wanted. They had no conscience, no morals, not an iota of mercy, even though she was a mere child."

The mother of one student said that the community around the university lived in fear when a visit from the dictator was announced.

"The girls he wanted would be rounded up and sent to him," she said.

Some were held for years, while others were dumped with appalling injuries.

The women would first be raped by the dictator then passed on, like used objects, to one of his sons Seham Sergewa, psychologist

"One just disappeared and they never found her again, despite her father and brothers searching for her. Another was found three months later, cut, raped and lying in the middle of a park. She had been left for dead."

Many would only speak to the film-makers on condition of anonymity, terrified of reprisals from those still loyal to the dictator, who was dragged from a drainpipe and shot by rebels in 2011.

Some victims were then drafted into 'the Haris al-Has' – private female bodyguard – enduring years of rape and abused and forced to witness the execution of opponents to the regime.

One former member recalled: "Early one morning, at 2am, we were taken to a closed hall. We were to witness the murder of 17 students. We were not allowed to scream. We were made to cheer and shout. To act as though delighted by this display. Inside I was crying. They shot them all, one by one."

Benghazi-based psychologist Seham Sergewa interviewed victims for the International Criminal Court, and said that as many as 400 women served in the unit over the years.

"A pattern emerged in their stories," she said. "The women would first be raped by the dictator then passed on, like used objects, to one of his sons and eventually to high-ranking officials for more abuse.

"In one case a girl of 18 said she was raped in front of her father. She kept begging her distraught father to look away. Many of the victims say they contemplated suicide many times. Doubtless there were some who took their own lives."

It was not just girls who were made to serve in Gaddafi's harem; boys were also abused.

He liked to keep his victims in the refrigerators to look at them now and again Baha Kikhia, wife of disappeared politician

"He was terribly sexually deviant. Young boys and so on. He had his own boys. They used to be called the 'services group'. All of them were boys and bodyguards . . . a harem for his pleasure," recalled former chief of protocol Nuri Al Mismari.

In making the film, the documentary makers also uncovered evidence that Gaddafi used a private hit squad based in Cuba to eliminate opponents, and kept the bodies of victims in freezers.

Baha Kikhia was the wife of a foreign minister who had a fractious relationship with the dictator and went missing. When Gaddafi's regime fell, she found out that her husband's body was among those stored.

"He liked to keep his victims in the refrigerators to look at them now and again," she said. "He would visit his victims. It was as though they were some sort of macabre souvenirs. Something that he could look at and touch to remind himself of his omnipotence. Some had been there as long as 25 years."

Allegations that Gaddafi kidnapped scores of women and subjected them to systematic abuse emerged last year, when French journalist Annick Cojean published Gaddafi's Harem: The Story of a Young Woman and the Abuses of Power in Libya, recounting the story of a girl kidnapped and raped by Gaddafi as a schoolgirl.

Storyville: Mad Dog – Gaddafi's Secret World will be shown in the UK on BBC4 at 10pm on 3 February.