Ten anti-slavery activists were arrested earlier this month in the town of Rosso, Mauritania — the country that has the highest rate of slavery in the world, according to a recent human rights group report.

Charged under Mauritania's terrorism laws with incitement to racial hatred, the activists now await trial in the capital Nouakchott. There, authorities last week detained a further two human rights defenders — this time for organizing protests calling for the release of their fellow campaigners.

Around 160,000 people in Mauritania are currently enslaved — roughly 4 percent of its population of 3.89 million — according to the 2014 Global Slavery Index released last week. That gives the sprawling north-west African nation the world's highest incidence of slavery — and campaigners say the government is doing nothing to end the practice.

The human rights defenders from the Resurgence of the Abolitionist Movement (IRA) were traveling along the Senegal River in Mauritania on November 11 when they were arrested. They were running an awareness campaign in the region to highlight the plight the plight of the Haratin, or Black Moors, an ethnic group that has historically be enslaved by Beydan masters, also known as White Moors.

The caravan started November 7, and enthusiastic crowds attended the group's workshops and meetings. Rosso, which straddles the border with Senegal, was meant to be the last stop on the tour. But authorities accused the IRA activists of using their rallies to disseminate "racist propaganda" and swiftly detained them. Following the arrests, police also shut down IRA headquarters in the capital.

At least five other IRA members have been arrested in the country this year, including three in the days leading up the caravan, according to a timeline of the arrests compiled by the Unrepresented Nations and People's organization.

IRA president and founder Biram Dah Abeid is one of the activists detained in Rosso. The son of freed slaves, 49-year-old Abeid received the 2013 UN Human Rights Prize for his work.

Abeid comes from a nomadic family that traveled from Mauritania to Senegal with the seasons, farming and raising livestock. After studying law and history, he did field work in Mauritania and became active in the anti-slavery NGO SOS Slaves. He ran as an opposition candidate in Mauritania's 2014 presidential election, but lost to incumbent Mohamad Abdel Aziz, who received 82 percent of the vote. Abeid later accused Aziz's ruling party of widespread electoral fraud in the contest.

Speaking to VICE News, Abeid's adviser, Hamady Lehbouss, explained the government's frustration with the groups' awareness campaign.

"The caravan bothered [officials] because it was very popular," he said. "It was pressurizing the government, who wanted to stop it from delivering its message to the slaves."

"The government is doing its best to protect the slave-holders," Lehbouss added, suggesting that some members of the country's establishment themselves kept slaves.

According to the latest slavery index by Australian NGO Walk Free an estimated 35.8 million people in the world are victims of modern-day slavery. While the largest numbers of slaves are found in India, Mauritania is the worst offender in terms of prevalence, partly because slavery in Mauritania is hereditary, and slave status can be passed down through the generations. According to the report, "slavery is deep-rooted in Mauritanian society."

The majority of slaves in Mauritania are Black Moors who are descended from sedentary ethnic groups along the Senegal River. Typically, they are enslaved by White Moors, whose ancestors were the Berber settlers who came to Mauritania in the 11th century.

Slaves live mostly in the desert, where they are forced to work in the fields. They have no access to schools, cannot inherit property or possessions, and need their masters' permission to marry. Those who escape from slavery have little legal recourse, and, according to Amnesty International, former slaves suffer tremendous discrimination.

Mauritania became the last country in the world to abolish slavery in 1981. The ban, however, was not enforced by criminal law until 2007, when the country's National Assembly unanimously voted to criminalize slavery. Under this law, anyone found owning slaves can be sentenced to 5 to 10 years in jail. But the law is rarely enforced.

The IRA, which was founded in 2008 to ensure compliance with the anti-slavery law, has never been formally recognized by the State, and is only marginally tolerated.

Alain Antil, a researcher at the French institute of International Relations, wrote in a May report that in Mauritania, "slavery has been, and continues to be, legitimized by a number of Ulemas (Islamic scholars)."

In 2012, Abeid was jailed for burning early Islamic Maliki texts that condoned slavery, for which he received a death sentence. Abeid was eventually released from jail, but his sentence has still not been formally revoked.

"Through this symbolic and provocative act, the movement mainly succeeded in bringing the issue of slavery to the forefront of politics, and in highlighting the fact that religious leaders have condoned this practice for centuries," Antil said.

The arrests took place in a tense political climate, following the June 2014 reelection of incumbent president Aziz. Speaking to VICE News, Mohamed Yahya Ould Ciré, head of the Association of Mauritanian Haratin in Europe, said that religion and slavery are entwined in the Islamic Republic of Mauritania.

"A month ago, an imam from the great mosque in Nouakchott called for the murder of abolitionist activists," said Ciré. "Some Islamists use Islam to justify slavery. It is not a coincidence that, shortly after this sermon, several militant abolitionists were arrested."

In October, four members of the IRA had been arrested for speaking out against the clerics. They were charged with disrupting prayers and attempting to start a revolution. They are still being detained, without ever having been tried.

On November 12, Amnesty International released a statement, urging an end to the crackdown on anti-slavery activists like Abeid. Speaking to VICE News from Dakar in Senegal, Amnesty International spokesperson Sadibou Maroug said that the NGO considers the arrest "to be part of a generalized [campaign of] repression that constitutes an infringement of the freedom of association."

Amnesty International has also highlighted the mistreatment of the detained activists at the hands of the police. The IRA has criticized the lack of care given to Dr. Saad Louleyd, one of the detained activists. "He was not given access to medication for six days even though he is diabetic," said a spokesperson for the group, "and he was not allowed to sleep or wash for 6 days."

The Mauritanian government has denounced what it describes as "political one-upmanship and manipulations" surrounding the question of slavery, telling newspaper Le Calame that the arguments are "divisive, and pose a threat to the national unity."

This week, Mauritanian president Aziz will be visiting Senegal to attend the Francophonie summit for leaders of French-speaking nations, whose mission is to promote "peace, democracy and human rights."