The appeal of 13 anti-slavery activists in Mauritania began Monday under heavy security as defence lawyers called for their case to be thrown out due to "legal inconsistencies", including torture in custody.

A court in Zouerate, northern Mauritania, will consider whether the sentences of three to 15 years in prison handed down in August to members of a group fighting hereditary slavery were justified.

Defence lawyer Bah Ould M'Bareck, acting for the members of the  Initiative for the Resurgence of the Abolitionist Movement (IRA), said his team had "raised the procedural exceptions that we judge to be sufficient to have (the case) thrown out."

The lawyer said the activists had been "submitted to torture" while in custody, an assertion repeatedly made by the accused themselves.

The court decided to add the procedural claims to the main case, which opened on Tuesday evening, with the first three accused pleading not guilty, M'Bareck said.

The case is due to continue on Tuesday with more accused giving evidence, followed by speeches from the prosecutors and defence lawyers.

The 13 were initially convicted by a judge in the capital, Nouakchott, of using violence, attacking security forces, gathering while armed and membership of an unrecognised organisation.

The campaigners were arrested between June 30 and July 9 after a protest by a Nouakchott slum community that was being forcibly relocated as the city prepared for an Arab League summit on July 25.

About 10 police officers were injured during the demonstration, according to local officials.

The slum was home to many so-called Haratin -- a "slave caste" under a hereditary system of servitude whose members are forced to work without pay as cattle herders and domestic servants, despite an official ban.

Seven of the slum's residents are also appealing against their sentences.

IRA supporters flooded the court on Monday, according to witnesses contacted by AFP, following a morning sit-in closely watched by police.

Rights group Amnesty International said in a statement ahead of the appeal that those convicted were not even present the day of the Nouakchott protest.

"This is an open and shut case of the government trying to silence anti-slavery activists in Mauritania," said Kine Fatim Diop, Amnesty International's West Africa campaigner.

"From the outset this trial has been marred by irregularities, and allegations of torture that have not been investigated," Diop added, calling the legal proceedings a "farce" that had not proved criminal responsibility on the part of the activists.

French lawyers for the IRA accused filed a criminal complaint in Paris for "torture and cruel treatment".

Source: AFP