The demonstrators converged at Independence Square in the heart of the city, following a call by a coalition of civil society associations on a day marking the country's 1960 independence from France.
The coup has triggered alarm bells in Western countries struggling to contain a jihadist insurgency that flared in northern Mali in 2012, advanced into Niger and Burkina Faso three years later and now threatens the borders of fragile states on the Gulf of Guinea.
France has some 1,500 troops in Niger in a bid to fight against jihadism in the Sahel.
