The human rights organisation Amnesty International has urged Zambia to drop charges against a gay couple “charged with the offence of sodomy or having sex against the order of nature” and release them from prison unconditionally.

James Mwape and Philip Mubiana were arrested in May after the family of one of the men reported the relationship to authorities.

Before facing trial, The Human Rights Watch previously urged authorities in Zambia to release two men.

In a court hearing on tuesday, Amnesty International has said it considers the two men “prisoners of conscience” as they were arrested under laws criminalising consensual, private, same-sex sexual activity, and such laws contravene international human rights law.

The organisation said it was also troubled by reports that on two occasions in May, government doctors forcibly conducted anal exams on both Mr Mwape and Mr Mubiana.

Simeon Mawanza, Amnesty’s Zambia researcher, said: “Anal exams are inherently invasive, abusive, profoundly humiliating and conducted for reasons based purely on discrimination.”

He added: “This procedure is not only scientifically illegitimate, it is also a form of sexual assault and is tantamount to torture. Any “findings” that result from it cannot be used as evidence in a trial against the victims.”

Mr Mawanza also said it is “high time” that individuals stop being persecuted because of sexual orientation or gender identity in Zambia.

He said: “Human rights are about the dignity and equality of all people.”

Mr Mwape and Mr Mubiana, both 22 years old, will appear in court on 12 September in the Zambian town of Kapiri Mposhi for a remand hearing. They have been held in custody since 6 May 2013.

Mr Mawanza said: “The arrest of anyone for their real or perceived sexual orientation violates the fundamental principle of non-discrimination which underlines human rights law.”

Thirty six countries in Africa currently criminalise gay sexual activity.

In July, an Englishman living in Zambia was forced to leave the country for good after details of his civil partnership in the UK generated a storm of controversy.