"This crime occurs within a framework of homophobia marked by the silent complicity of authorities to incidents involving many individuals and organisations defending the rights of sexual minorities," 11 human rights groups said in a statement on Saturday.
Eric Lembembe was found dead in his home in the capital Yaoundé on Monday, and friends who found his body said he had been severely tortured.
Homosexuality is considered a crime in the west African country and punishable by up to five years in prison.
The government vowed on Friday to conduct a full investigation, dismissing fears that the murder would go unpunished.
"There is no conspiracy of state, nor any social plot in Cameroon, which is directed toward homosexuals," government spokesperson and Communication Minister Issa Tchiroma Bakary said on state television.
"Many homosexuals live and move freely in Cameroon without being beaten or suffering punishment."
Botching the investigation
Bakary said an autopsy had been ordered and data requests had been sent to mobile phone operators.
Lembembe's lawyers had on Thursday accused the police of botching the investigation, charging that they had "done nothing" to collect potential evidence after the discovery of the body.
The rights groups on Saturday asked President Paul Biya to use the constitution to "take strong measures to stop this wave of hatred and to protect a minority of Cameroonian citizens that is persecuted".
"The religious authorities, the Cameroonian Roman Catholic Church in particular, take a position on homosexuality in order to incite violence," their statement charged. – AFP