Slavery is believed to affect between 4 and 20 percent of the population in Mauritania

NOUAKCHOTT, July 3 (Reuters) - Mauritanian authorities have arrested nine anti-slavery activists and accused them of starting a riot in which several police officers were injured and a bus was burned, activist leaders said on Sunday.

The arrests were an attempt to use the riot in Nouakchott to discredit the Initiative for the Resurgence of the Abolitionist Movement (IRA) movement, its coordinator Issa Ould Aliyine told a news conference.

"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," he said.

The riot on Wednesday started when police moved squatters from the Haratin ethnic group, many of them former slaves, from an area they have occupied illegally for decades, said Cheikh Sid'Ahmed Ould Sidi, the prefect of Ksar where the clash took place.

The Haratin, Mauritania's main "slave caste", are descended from ethnic groups along the Senegal river. They often work as cattle herders and domestic servants.

"What happened was provoked by a movement known for its extremism," said Mahy Ould Ahmed, one of the governors of the capital Nouakchott, referring to the IRA. It was not clear whether the activists were charged.

Slavery is a crime against humanity in Mauritania but the practice is still believed to affect between 4 and 20 percent of the population. Anti-slavery activists are frequently at odds with the government. (Reporting by Kissima Diagana; Writing by Matthew Mpoke Bigg; Editing by Tom Heneghan)

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