Egyptian police have arrested four men suspected of being HIV positive, bringing the total detained in a recent crackdown to 12, rights groups say.
Men accused of being homosexual are tortured by police, HRW alleges
Human Rights Watch (HRW) said last week that HIV-positive Egyptian men had been chained to hospital beds and forced to undergo tests for the virus.
The latest arrests took place after police followed up information coerced from men already detained, HRW said.
The Egyptian interior ministry has not responded to the allegations.
In a joint press release, Amnesty International and HRW warned that Egypt's efforts to prevent the spread of the deadly virus could be seriously damaged by the arrests.
"This not only violates the most basic rights of people living with HIV. It also threatens public health, by making it dangerous for anyone to seek information about HIV prevention or treatment," said Rebecca Schleifer, who works on HIV/Aids issues at HRW.
Two of the newly-detained men tested positive for HIV, and are awaiting further hearings, HRW said.
The rights organisations say a wave of arrests began in October 2007, when two men were arrested after a scuffle in central Cairo.
When one said he was HIV-positive they were taken to the police branch which deals with issues of public morality, HRW said.
Both men said they had been beaten for refusing to sign statements written by the police and subjected to anal examinations to "prove" that they had engaged in homosexual conduct, the group said.
Two more men were arrested when police found their photographs and contact numbers in the wallets of those detained, HRW said.
All four men, who have not been identified, remain in custody pending a prosecutor's decision on possible charges.
Four further arrests were made in November when police raided the flat of one of those being held, which had been placed under surveillance, HRW reports.
Those four men were sentenced to one year in jail in January having been convicted of "habitual debauchery", which Human Rights Watch says is a euphemism used to penalise consensual homosexual acts.
Their lawyers claimed the prosecution had produced no evidence against the defendants, who pleaded not guilty.
All those who have tested positive have been held, chained to their beds, in Cairo hospitals, the rights groups said.
While not explicitly referred to in Egypt's legal code, homosexuality can be punished under several different laws covering obscenity, prostitution and debauchery.
Egypt has come under repeated criticism by both human rights groups and the international community for its treatment of homosexual people.
"These cases show Egyptian police acting on the dangerous belief that HIV is not a condition to be treated but a crime to be punished," Gasser Abdel-Razek, HRW's acting director of regional relations in the Middle East, told the BBC.