Thousands of Mauritanians rallied in the capital Nouakchott on Wednesday to protest against nationwide elections later this month that have been dismissed by the opposition as a sham.

"Unilateral elections kill democracy," the demonstrators chanted, as they marched through the city centre, an AFP reporter saw. No incidents were reported during the protest, which was closely watched by security forces.

The demo was organised by the umbrella Coordination of Democratic Opposition (COD), 10 of whose 11 parties are boycotting what they call an "electoral masquerade" after talks on how the vote should be run broke down last month.

Around a third of Mauritania's 3.4 million people are eligible to vote in the first parliamentary and local polls since 2006, five years after the coup of junta chief Mohamed Ould Abdel Aziz, who was eventually elected in widely-contested polls.

"The elections are stillborn, and we won't do anything that could give them life, on the contrary, we will make them fail," Mohamed Ould Khlil, a COD member, told AFP.

The protest took place on the eve of the official start of the two-week election campaign.

The ruling Union for the Republic is the only party fielding candidates in all 218 constituencies.

Mauritania, a mainly-Muslim republic, is a former French colony on the west coast of the Sahara desert. It is seen by Western leaders as strategically important in the fight against Al-Qaeda-linked groups within its own borders, in neighbouring Mali and across Africa's Sahel region.