Dozens of young Mauritanians are holding a sit-in outside the police directorate's office to demand the release of 20 protesters arrested the previous day.
Youth on Tuesday chanted "freedom for our friends" before dispersing peacefully.
Mauritanian police arrested 20 people on Monday after hundreds demonstrated in the capital against the regime of President Mohamed Ould Abdel Aziz. Police said the demonstrations were unauthorized and used tear gas and batons to disperse people.
Demonstrations have been ongoing since Feb. 25, when dozens of students used Facebook to organize another sit-in demanding political reforms and the president's departure.
In January, a businessman died after setting himself ablaze in a protest against the government.