* Lembembe found dead in home, neck broken, face burned
* Latest attack on gay rights campaigners
* Past investigations have failed to find suspects - groups
Campaign groups urged Cameroon to carry out a thorough investigation into the brutal killing of a gay rights activist, the latest attack on people fighting to legalise homosexuality in the central African country.
Friends found journalist Eric Ohena Lembembe dead in his home in the capital Yaounde on Monday. His neck was broken, his feet smashed and his face burned with a clothes iron, Human Rights Watch said.
Lembembe's murder came less than two weeks after he released a statement condemning attacks by "anti-gay thugs".
The police said they had already opened an investigation.
"It is true that lesbianism, gay and bisexual behaviour ... is against the penal code of our country but this does not demand that people should go as far as killing those involved," a senior police officer told Reuters. Homosexuality is illegal in many parts of Africa.
But Human Rights Watch said past investigations into similar attacks had failed to find any suspects.
"Every day we are witnessing serious human rights violations yet the authorities are not taking strong measures to combat it," said lawyer and gay rights activist Alice Nkom, who has herself received death threats.
The Cameroon Association for the Defence of Homosexuality called on the government to guarantee the safety of gay people.
Lembembe was the executive director of the Cameroonian Foundation for AIDS.
He also helped research a Human Rights Watch report released in March detailing systematic abuses of homosexual people and campaigners, including discriminatory treatment by officials, illegal arrests and torture.
Washington and Paris joined other world powers in expressing concern over the killing.