Flight tracking website Flightradar24 is showing that there are currently no aircraft in Niger’s skies.
The West African group of countries, Ecowas, had earlier warned it could use force if President Mohamed Bazoum was not reinstated by 23:00 GMT on Sunday.
A junta spokesman says Niger’s armed forces are ready to defend the country.
Mr Bazoum was detained on 26 July, and Gen Abdourahmane Tchiani, commander of the presidential guard, later proclaimed himself the new leader.
The military takeover has been internationally condemned, including by former colonial power France and the rest of the European Union, as well as the United Nations and the United States.