Niger President Mamadou Tandja and his cabinet are being held by soldiers after gun battles in the capital, a government source has told the BBC.
Gunfire broke out around the presidential palace at about 1300 (1200 GMT) and continued for 30 minutes, says the BBC's Idy Baraou in Niamey.
Our correspondent says tanks have been firing and witnesses report seeing injured people being taken to hospital.
Tensions have been growing in the uranium-rich nation since last year.

Mr Tandja was widely criticised when he changed the constitution in August to allow him to stand for a third term.

An unnamed French official told AFP that a coup attempt was under way.
"All I can say is that it would appear that Tandja is not in a good position," he told the news agency on condition of anonymity.

The exchange of gunfire has been between soldiers but it is confusing and one cannot tell one side from another. I saw tanks being fired and soldiers on the streets using machine guns.

The area near the presidential palace is where the business of government takes place and at least four military barracks are based there.

People have fled the area and some civil servants have locked themselves inside their offices.

Earlier, smoke could be seen from the roof of the office where President Mamadou Tandja was holding his cabinet meeting.

Soldiers captured Mr Tandja while he was chairing his weekly cabinet meeting, the government source said.

But Reuters news agency spoke to other people inside the palace who said things were "all right".

"We can hear gunshots from time to time but... the president is in his office," a security source told Reuters by telephone.

Our correspondent says sporadic shooting can still be heard.

A witness told AFP that the bodies of three soldiers had been taken to a military mortuary.

But the situation in Niamey remains unclear, with radio stations continuing their programmes as normal and apparently there has been no large-scale deployment of military personnel.

The government and opposition have been holding on-off talks since December - mediated by the regional body Ecowas - to try to resolve the country's political crisis.

Mr Tandja, a former army officer, was first voted into office in 1999 and was returned to power in an election in 2004.

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, work has begun on the world's second-biggest uranium mine, and energy deals have been signed with Chinese firms.