DAKAR (Thomson Reuters Foundation) - Mauritanian anti-slavery activists jailed last month have been tortured in detention and transferred to a remote desert location in an “intensification of repression” by the state, a leading campaigner said.

The West African nation in August jailed 13 members of the Resurgence of the Abolitionist Movement (IRA) for up to 15 years for their role in June protests by residents of a slum in the capital Nouakchott, many of whom are former slaves.

Slavery is a historical practice in Mauritania, which became the last country worldwide to legally abolish it in 1981.

Today some 43,000 people or at least one percent of the population live as slaves, according to the 2016 Global Slavery Index. Yet other estimates put the number as high as 20 percent in a country that is a focus of activism by the modern anti-slavery movement.

The 13 activists have been tortured and were this week moved to the desert north where they are cut off from their families, doctors, and lawyers, according to members of the IRA in the northern town of Zouerate who were informed of the relocation.

Mauritanian government officials did not respond for requests to comment.

“This intensification of repression is equal to the intensification of the fight (against slavery),” Biram Dah Abeid, head of the IRA and an opposition politician, told the Thomson Reuters Foundation in Dakar, Senegal.

“Our colleagues suffered physical and psychological harm,” he said, adding that people cannot even visit the prisoners’ families for fear of being watched by the government.

The activists said they were not present at the protests and that the trial was an attempt by the state to discredit the IRA.

Anti-Slavery International called the sentences a “devastating blow” to the Mauritanian anti-slavery movement.

A European Union delegation said last month it was concerned by “credible allegations” of torture and violations of legal procedures in the case against the activists, and urged the Mauritanian authorities to investigate.

The Haratin, who make up Mauritania’s main “slave caste”, are descended from black African ethnic groups along the Senegal river. They often work as cattle herders and domestic servants.

The West African nation criminalized slavery in 2007 and a new law passed last year makes the offence a crime against humanity and doubles the prison term for offenders to 20 years.

The jailing of two slave-owners in May and the release of Abeid and activist Brahim Bilal, who had been in prison for 18 months after taking part in an anti-slavery march, were hailed as a turning point in the fight to end the practice.

But Abeid, who has been jailed several times and came a distant second in a 2014 presidential election, said the moves were merely “an illusion” of progress.