"He pointed the laser sight directly in the middle of my chest," said Professor Shaker, a political scientist at Baghdad University. "Then he pointed to his penis. He told me, 'Come here, bitch, I'm going to fuck you.'"

The incident is one of a number in which US soldiers are alleged to have abused, intimidated or sexually humiliated Iraqi women.

According to Prof Shaker, several women held in Abu Ghraib jail were sexually abused, including one who was raped by an American military policeman and became pregnant. She has now disappeared.

Most of the coverage of the prisoner abuse at Abu Ghraib has focused on Iraqi men. But there is compelling evidence that several female prisoners, who are in a minority at the jail, were abused as well.

"A female colleague of mine was arrested and taken there. When I asked her after she was released what happened at Abu Ghraib she started crying," Prof Shaker said.

"Ladies here are afraid and shy of talking about such subjects. They say everything is OK. Even in a very advanced society in the west it is very difficult to talk about rape. But I think it happened."

Few women released from US detention have come forward to talk about their experiences in a Muslim society where rape is sometimes equated with shame and victims can be killed to salvage family honour.

According to the New Yorker magazine the photos and videos so far unreleased by the Pentagon show American soldiers "having sex with a female Iraqi prisoner", and a secret report by General Antonio Taguba into the scandal confirms that US guards videotaped and photographed naked female prisoners and that "a male MP [military police] guard" is shown "having sex with a female detainee".

Yesterday Prof Shaker, who began researching the subject this year for Amnesty International, said she believed the woman involved had been killed.

"The girl was called Noor. When I went to her house in Baghdad earlier this year she had disappeared. The neighbours said that she and her family had moved away."

Since the US military began its inquiry into prisoner abuse in January, many female detainees have been released from Abu Ghraib and the other US detention facilities across Iraq.

But five women are still in solitary confinement in Abu Ghraib's notorious 1A cellblock where as many as 1,500 pictures were taken in November and December.

According to Rajaa Habib Khuzaai, an obstetrician who is one of three women on the US-appointed Iraqi governing council, none of the five has been raped or sexually abused. US officials allowed Dr Khuzaai to visit them yesterday and interview them privately.

Two of the women told her that US soldiers had beaten them after their arrest in December and January while they were in custody at Baghdad international airport, before their transfer to Abu Ghraib.

"They were a little embarrassed. They merely said they had been beaten and that was it," Dr Khuzaai told the Guardian.

She added: "They are now paid special attention. Conditions are OK and they have given them some privacy."

But there are unanswered questions as to why the women have been locked up without charge.

According to Dr Khuzaai, two of the women are married to high-ranking and absconding Ba'ath party officials, two are accused of financing the Iraqi resistance, and one had a relationship with the director of Iraq's former secret police, the mukhabarat.

Human rights campaigners say the US military frequently arrests wives and daughters during raids if the male suspect is not at home.

US officials have acknowledged detaining women in the hope of convincing male relatives to provide information: a strategy that is in violation of international law.

"The issue is the system," Nada Doumani of the International Committee of the Red Cross said yesterday.

"It is an absence of judicial guarantees. People are being kept in custody without knowing what for. The system is not fair, precise or properly defined."

Senior US military officers who escorted journalists around Abu Ghraib on Monday admitted that rape had taken place in the cellblock where 19 "high-value" male detainees are also being held.

Asked how it could have happened, Colonel Dave Quantock, who is now in charge of the prison's detention facilities, said: "I don't know. It's all about leadership. Apparently it wasn't there."

Journalists were forbidden from talking to the women, who are kept upstairs in windowless 2.5 metre by 1.5 metre cells. The women wailed and shouted.

They were kept in solitary confinement for 23 hours a day, Col Quantock said, with only a Koran.

Other allegations being investigated are that a 12- or 13-year-old girl had been stripped naked in the block and paraded in front of male inmates.

Yesterday Prof Shaker said after her ordeal in February her friends dragged her back into the car and drove off. "I vowed never to talk to another American soldier," she said.