Foreign detainees in at least one United Arab Emirates (UAE) prison are being denied lifesaving HIV treatment, according to Human Rights Watch.
Former prisoners of Dubai's central jail told the group that treatment was often delayed, interrupted or denied altogether.
International guidelines on human rights in prisons say inmates have a right to medical services.
The UAE has categorically rejected the allegations.
A statement sent to the BBC said: "The UAE is determined to uphold the highest standards on the treatment of prisoners and does not discriminate against individuals on the basis of health conditions, in line with our commitment to global human rights."
Human Rights Watch (HRW) said in a statement that non-citizen prisoners were not given the same access to treatment as Emirati prisoners in Dubai's Al Awir Central Jail.
"The UAE has an obligation to provide health care, including antiretroviral medicines, to all prisoners in their custody without discrimination," said Michael Page, HRW's deputy Middle East director.
Foreign HIV-positive prisoners previously held at Al Awir said they received regular testing every three to six months, but were not granted consistent access to treatment.
They also said prison officials were "indifferent" to requests for care, and that some prisoners were detained without charge because they had tested positive for HIV.
Prisoners with HIV are kept separate from other inmates and report experiencing stigma and systemic discrimination.
One source told HRW that a prisoner recently fell ill after nearly four months without treatment, and had test results showing warning signs for the onset of Aids.
As a member state of the United Nations, the UAE is committed to a worldwide effort to end Aids by 2030.
UN standards on human rights and prisons state that prisoners should be provided with necessary medical treatment.
They said Ahmed Mansoor - imprisoned for "defaming" the country on social media - had no bed or water in his cell and was subject to prolonged periods of solitary confinement that might amount to torture.