A pregnant teenager who says she was gang-raped has been charged with adultery in Sudan, and faces a possible sentence of death by stoning. The country's judiciary has received millions of pounds in aid from the UK.

The 18-year-old Ethiopian, who is nine months pregnant, is being held in a police cell and until recently was sleeping on a bare concrete floor without a mattress or suitable food or clothing, according to the Strategic Initiative for Women in the Horn of Africa (SIHA) network.

SIHA accused Sudan of discriminating against the alleged victim because she is both a woman and a migrant, and demanded her immediate release or transfer to hospital.

The young divorcee claims that last August, when she was about three months pregnant, she was lured to an empty property in the capital, Khartoum, and violently gang-raped by seven men. She reported the incident to a police officer at the time, but he decided against pursuing an investigation because of the Eid holiday. He was initially charged with negligence, but this was dropped on Tuesday.

According to SIHA, the attack was filmed by one of the men on his phone and circulated on social media six months later, leading to the arrest of both the alleged perpetrators and victim. The case came to court earlier this month. Five men, understood to be between 18 to 22, are accused of adultery; a sixth, who says he did not have sex with the woman, is accused of gross indecency.

The woman is charged with adultery, although she denied the charges and is pleading not guilty on the basis that the sexual act was against her will. Her attempt to make a complaint of rape has been denied on the technicality that she is under investigation on other charges and she should have complained at the time of the incident. Her request for bail has been denied by the attorney general.

"The intention to place culpability on the part of the victim is of great concern and seeks to deflect and reduce accountability of the perpetrators, but more disturbing is that the charge of adultery carries with it the potential sentence of death by stoning if found guilty," SIHA said.

Although rarely carried out, SIHA noted, the sentence of stoning for adultery has been handed down twice in recent years, against two women, Intisar Sharif and Laila Jamool, in 2012. Following appeals in both cases, the sentences were overturned.

The Sudanese government has been criticised for the mistreatment and marginalisation of foreign nationals, with Ethiopians often a target of xenophobia. SIHA said the Sudanese media has sought to undermine the alleged rape victim by falsely claiming that she has HIV and stating that she is a prostitute. "There have even been cynical attempts to falsely claim that the men were accidently prescribed hallucinogenic drugs by a chemist beforehand."

Hala Alkarib, regional director of the SIHA network, said: "Impunity and silence on crimes of sexual violence committed against IDPs [internally displaced persons], migrants and impoverished women in Sudan has been a pattern for years.

"This case brings to light the obstacles in bringing complaints of rape, let alone negotiating the legal system through to prosecution. There is an urgent need for article 149 of the criminal code referring to rape to be reformed to protect victims and pursue justice."

She added: "Successful prosecution of rape is the exception as opposed to the norm and most certainly does not reflect the level of incidence. Instead victims face the risk that they will instead be prosecuted for adultery, being re-vicitmised by the judicial system, and threatened with the ultimate sentence of death by stoning."

The case is likely to raise questions over Britain's donor support for the justice system in Sudan. A Department for International Development (DfID) document says it will provide up to £20.6m over the period March 2010 to March 2014 to fund a "safety and access to justice programme" in Sudan and South Sudan.

The programme is intended to support rule of law partners to "improve the daily experience of people requiring access to security and justice through infrastructure development and by strengthening the institutions' ability to respond effectively and efficiently to the requirements of social peace and tranquillity".

But the support to Sudan was cut off last month, earlier than planned. A DfID spokesman said on Tuesday: "We condemn absolutely all human rights abuses and stoning is an abhorrent practice. DfID recently ended its support to the Sudanese judiciary in light of the deteriorating operating environment and our deep concerns about human rights abuses."

Last year a Somali woman who alleged she was raped was sentenced to a year in jail. She was later acquitted after a worldwide outcry.