Sidi Muhammad Walad Maham was taken into custody on Monday on charges of contempt for what the court president called his "insolence" at the start of the trial of suspects accused in three alleged plots to oust the pro-western government of President Muawia Sid Ahmad Walad Taya.
After spending most of the day at a police station near the desert town of Wad Naga, where the 172 suspects in custody are being detained at a prison 50km east of the capital Nouakchott, Walad Maham was transported to another facility at Rosso on the border with Senegal.
Walad Maham was representing some of the suspects in court.
"We have opted to boycott all of the court sessions in the country after the actions taken against our colleague, who we demand be released immediately," the lawyers said in a statement on Tuesday.
"We strongly denounce his detention and demand that the accusations levelled by the court against Walad Maham be judged immediately."
"We strongly denounce his detention and demand that the accusations levelled by the court against Uld Maham be judged immediately"
Statement by lawyers
The defendants - including ranking officers, an ex-president and two heads of opposition parties - are accused of mounting three coup plots between June 2003 and September 2004. They face death if convicted.
The plots targeted the 20-year-old regime of President Taya, who himself took power in a coup.