More than a dozen human rights groups are calling on Mauritania to unconditionally release 13 anti-slavery activists and drop all charges against them.

Amnesty International said Monday the activists have been falsely accused. The organizations called for their release ahead of a court appearance Wednesday.

The activists, members of a non-governmental organization that campaigns against slavery in the West African country, are accused of armed assembly, use of violence, attack against public authority and rebellion. They were arrested between the end of June and early July after a protest against the relocation of a slum community.

Mauritania outlawed slavery in 2007, but the practice persists and slavery convictions remain rare.