Several thousand people protested in Gabon on Saturday against a spate of ritual killings that has seen mutilated bodies washing up on beaches in the central African state this year.
Sylvia Bongo, Gabon's first lady, led most of the demonstrators, while rights groups tried to lead a separate march but members said they were dispersed by tear gas and several leaders arrested by the security forces.
Body parts of humans and animals are prized by some in the region and Gabon's Association for the Prevention of Ritual Crimes estimates that 20 people have been killed so far this year and their lips, tongues, genitals and other organs removed.
President Ali Bongo, who addressed the main body of protesters, said: "Anyone who is convicted will be jailed for life, without the chance of parole. We must put an end to this phenomenon that tarnishes the image of our country."
But the rash of killings this year has led to accusations by rights groups that Bongo's government has not done enough to tackle the issue.
Several hundred people tried to take part in a separate demonstration from the one led by Bongo's wife, according to witnesses.
"The police fired tear gas to disperse the demonstrators," said Anne Lea Maye, a member of Gabon's Coalition of Women Against Ritual Killings.
Six senior figures from rights groups leading the rival march were arrested, said Marc Ona, a senior member of the movement.
The Interior Ministry had earlier said only the Bongo-led march would be authorised.
Critics say that until recently few in the closed-door power circles in Gabon would comment on the issue of ritual killings.
In the most high-profile ritual murder court case in Gabon to date, a convicted killer accused a Gabonese senator of ordering the 2009 murder of a 12-year-old girl for her organs.