Three jailed Mauritanian anti-slavery activists went on hunger strike Monday to protest their treatment by prison authorities, their campaign group said in a statement.

Biram Ould Dah Ould Abeid, the runner-up in 2014 presidential elections, is serving two years in the central Aleg prison, along with aide Bilal Ramdane and Djiby Sow, a civic and cultural rights campaigner.

Mauritania has postponed its senatorial elections to focus on persuading the opposition to drop plans to boycott the vote, the government has announced.

A first round of polls had been planned for March 15 but the opposition National Forum for Democracy and Unity (FNDU) coalition announced last month it would not take part.

Thousands of people took to the streets of Nouakchott on Friday to  protest against a cartoon of the prophet Mohammed published in the latest edition of the French Charlie Hebdo weekly.

The protesters set fire to a French flag but were prevented by security forces from reaching the French embassy in the Mauritanian capital, witnesses said.

Police in Mauritania used tear gas to disperse protestors, after three anti-slavery activists were sentenced to two years in prison on Thursday. 

Biram Ould Dah Ould Abeid, the runner-up in 2014 presidential elections and the head of an anti-slavery group, was convicted along with one of his aides Bilal Ramdane, and Djiby Sow, a civic and cultural rights campaigner.

Suspected Islamist militants killed one person in an attack in central Mali on Wednesday, two days after 11 troops were killed in an assault on a nearby military base, local officials.

The latest attack took place in Djoura, a village close to the border with Mauritania, about 465 kilometers (290 miles) northeast of the capital Bamako.

Lawyers for a Mauritanian man condemned to death for apostasy on Friday are to challenge his conviction for writing an article deemed blasphemous of Islam.

Mauritania has delivered its first death sentence for apostasy since independence in 1960, ordering capital punishment for a Muslim man who wrote an article deemed blasphemous of Islam.

Mohamed Cheikh Ould Mohamed, aged in his late 20s, fainted when the ruling was read out late Wednesday in a court in Nouadhibou in the northwest of the country, a judicial source told AFP.

Leaders in the sub-Saharan Sahel region of Africa called Friday on the United Nations to organize an international force "to neutralize the armed groups" sowing chaos in Libya.

The French army said Thursday it had killed the commander of a major West African jihadist group's branch in Mali in an operation in the north of the country.

Ahmed el Tilemsi was the emir of the Al-Murabitoun group in Mali and was earlier this year declared a "specially designated global terrorist" by the U.S. State Department, who offered a $5 million reward (four million euros) for information leading to his capture.

Mauritania's highest court on Sunday confirmed the victory of incumbent leader Mohamed Ould Abdel Aziz in presidential polls, and rejected an appeal calling for the results to be annulled.

"The candidate Mohamed Ould Abdel Aziz was elected President of the Islamic Republic of Mauritania in the first round of the presidential election," the chairman of the constitutional council, Sgheyir Ould M'barek, said during an official ceremony.