More than a dozen anti-slavery activists in Mauritania have been sentenced to up to 15 years in prison despite calls from human rights activists to release them and reports that they have been tortured.

The criminal court in the capital city Nouakchott passed sentences of between 3 and 15 years, according to local reports. The 13 activists from the Resurgence of the Abolitionist Movement (IfRA) had been charged with rebellion, violence, and 'membership of an unrecognised organisation' due to some local riots earlier in the year, though Amnesty International said they had not been present at the disturbance.

Amnesty had previously called on the West African country's authorities to release the activists. Lawyers for the activists had boycotted the proceedings due to reports that the detainees have endured torture.

Mauritania has one of the highest levels of slavery in the world, according to the World Slavery Index, with around 1 per cent of its population enslaved.

The IfRA claims that the government is trying to discredit its movement by linking it to the riots, according to the news agency Reuters. "From the first hours of the riots, and even without knowing their cause or the details, an order was given to government media to start a campaign to link the IRA with the violence," said IfRA spokesperson Issa Ould Aliyine at a news conference.

The riots had started after police moved squatters and former slaves from an area where they had been living illegally for decades.

Though slavery was officially abolished in Mauritania in 1981, and is against the law, anti-slavery organisations continue to document cases in the country, Amnesty said, though the government frequently opposes their activity.