African Union President and Mauritania President Mohamed Ould Abdel Aziz talks during a joint press alongside the African Union Commission Chairperson, the European Union Council president, and EU Commission President on the second day of 4th EU-Africa summit on April 3, 2014, at the EU Headquarters in Brussels. Some 80 nations are gathering in Brussels for an EU-Africa summit dominated by conflict, trade and illegal migration. AFP PHOTO / JOHN THYS (Photo credit should read JOHN THYS/AFP/Getty Images)

By Kissima Diagana

NOUAKCHOTT, Dec 25 (Reuters) - Mauritania on Thursday condemned a man to death for "insulting the prophet," a human rights group said, a day after the country opened the trial of an anti-slavery activist.

Mohamed Cheikh Ould Mkhaitir, 28, was arrested a year ago for writing an article about the Prophet Mohammad and the caste system, an extremely sensitive subject in a West African country with deep social and racial divisions.

He claims his article has been misinterpreted.

The prosecution asked for the death penalty to be carried out in accordance with Islamic sharia law and recommended he be shot. Mauritania, a poor country straddling Arab and black Africa, last applied the death penalty in 1987.

Separately, a court in the southern town of Rosso began proceedings on Wednesday against anti-slavery campaigner Biram Ould Dah Ould Abeiday and six members of his organization for "inciting violence, disrupting public order, contempt for authorities and membership of a non-recognized organization."

Biram Ould Abeid, a former presidential candidate, was arrested last month during a peaceful march. He could face a prison sentence of up to five years.

Human rights campaigners and the European Parliament have called for his release.

Mauritania became the last country worldwide to legally abolish slavery in 1981 and still has the highest prevalence worldwide of slavery per head of population, according to the Global Slavery Index 2013.

President Mohamed Ould Abdel Aziz denies slavery exists in his country, saying that only the consequences of this former practice exist. (Writing by Emma Farge; editing by Andrew Roche)