DAKAR, Senegal (AP) — International rights groups are urging Mauritania to release anti-slavery activists, as the United States has announced it will end trade benefits to the West African country over the continuation of slavery.

Amnesty International and other rights groups Thursday called for the release of anti-slavery campaigners, including a blogger, who remains in custody despite having served his sentence. It called for Mauritania's financial and technical partners to apply more pressure.

The U.S. said this month that Mauritania is not making sufficient progress toward combating forced labor, including slavery, and as a result it will end trade benefits under the African Growth and Opportunity Act, which permits some duty-free trade.

Mauritania was the last country in the world to abolish slavery in 1981, though the practice remains, affecting more than 90,000 people.