Col Goukoye Abdul Karimou read a statement signed by Col Salou Djibo
The African Union has condemned a coup in Niger, where soldiers have detained President Mamadou Tandja.
AU chief Jean Ping said he was watching developments "with concern" after a day of gun battles culminated in a takeover led by Colonel Salou Djibo.
West African bloc Ecowas "roundly condemned" the coup and dispatched a mission to talk to the plotters.
But one opposition activist told the BBC the soldiers were "honest patriots" who were fighting tyranny.
Heavy artillery
Mr Tandja provoked a political crisis last August when he changed the constitution of the uranium-rich country to allow him to remain in power indefinitely.
 | NIGER  Chronic poverty Population 14 million, 61% live on less than $1 a day Resource rich Huge reserves of uranium, Chinese firms digging for oil Politcally unstable History of coups, assassinations and on-off rebellion by nomadic Tuareg people in the north Source: World Bank  Country profile: Niger |
The Economic Community Of West African States (Ecowas), which suspended Niger after Mr Tandja's actions, said it had "zero tolerance" for any unconstitutional changes of government.
"We condemn the coup d'etat just as we condemn the constitutional coup d'etat by Tandja," Ecowas official Abdel Fatau Musa told the BBC's Network Africa programme.
He said the group had already sent a team to Niger and would maintain sanctions "until constitutional order is restored".
The BBC's Idy Baraou in the capital, Niamey, said on the morning after the coup, people in the city were going to mosques and shops as normal.
He said there was not an obvious military presence on the streets, but heavy artillery had been deployed around the presidential palace.
While state radio has been broadcasting military music overnight, state TV station Tele Sahel is continuing with live programming from a traditional wrestling championship.
Freedom fighters?
In a televised address on Thursday evening, a spokesman for the plotters announced that the constitution had been suspended and all state institutions dissolved.
The junta, which has called itself the Supreme Council for the Restoration of Democracy, imposed a curfew and closed the country's borders.
| NIGER JUNTA Col Salou Djibo Coup leader Col Djibrilla Hima Hamidou Involved in 1999 coup Col Goukoye Abdul Karimou Junta spokesman Col Amadou Harouna |
The plotters said their aim was to restore democracy and save the population from "poverty, deception and corruption".
The move came after gunfights around the presidential palace reportedly resulted in several fatalities.
Soldiers captured Mr Tandja while he was chairing his weekly cabinet meeting, a government source told the BBC.
Little is known about coup leader Col Djibo, but another of the plotters, Col Djibrilla Hima Hamidou, was junta spokesman during the last military takeover in 1999.
The president was assassinated during that coup, but civilian rule was restored within a year.
One opposition activist, Mahamadou Karijo, whose Party for Democracy and Socialism has been bitterly opposed to Mr Tandja's rule, praised the soldiers for fighting tyranny.
"They behave like they say - they are not interested in political leadership, they will fight to save the Nigerien people from any kind of tyranny," he told Network Africa.
History of instability
The government and opposition had been holding on-off talks since December to try to resolve the country's political crisis.
|  Profile: Mamadou Tandja |
Mr Tandja, a former army officer, was first voted into office in 1999 and was returned to power in an election in 2004.
His current whereabouts are unknown, but soldiers are thought to be holding him at a military base on the outskirts of Niamey.
Niger has experienced long periods of military rule since independence from France in 1960.
It is one of the world's poorest countries, but Mr Tandja's supporters argue that his decade in power has brought a measure of economic stability.
Under his tenure, the French energy firm Areva has begun work on the world's second-biggest uranium mine - ploughing an estimated $1.5bn into the project.
China National Petroleum Corporation signed a $5bn deal in 2008 to pump oil within three years.
