Ould Taya himself came to power in a coup

They are protesting at the detention on Monday of one of the lawyers representing the defendants.

Sidi Mohamed Ould Maham was accused of "insolence" by the court's president.

Ex-president Mohamed Khouna Ould Haidallah is among three opposition leaders charged with planning to oust Maaouiya Sidi Ahmed Ould Taya.

Non-lawyers appointed

"We strongly denounce his detention," the lawyers said in a statement.

They said they would boycott all court rooms in the country until their colleague was released.

Ould Maham was arrested on the first day of the trial.

His detention stemmed from a plea to the court's president on behalf of the lawyers defending the alleged coup plotters to "take seriously this solemn audience as human lives are at stake", AFP news agency reports.

The judge appointed two non-lawyers as the new defence, replacing more than 60 defence lawyers who walked out of the court in Wad Naga, 50km from the capital Nouakchott.

Recent months have seen an upsurge in insecurity in the soon-to-be oil rich country, with numerous alleged coup plots denounced by the government.

However, BBC correspondent Pascale Harter who has recently returned from Mauritania says lawyers for the defendants say the trial is a political attempt to silence opposition to a government they allege is corrupt and tribally affiliated.