Soldiers opened fire Thursday in the Niger capital -- where explosions and long bursts of gunfire resounded across the city -- in what a top French official said was an coup attempt against President Mamadou Tandja.

Witnesses said the firing appeared to be centred on the presidency. State radio stayed silent on events, concentrating on playing traditional music as tensions erupted in the uranium-rich West African nation.

Tandja, 71, has spent more than a decade in power, having extended his term through a controversial referendum last August after dissolving parliament and the constitutional court. Niger has since been isolated on the international stage.

It was not immediately known where Tandja was.

France urged its nationals to stay indoors.

"We heard automatic gunfire and then large detonations. The house was shaking. It lasted about a half hour, non-stop," said Claire Deschamps, one French national living in Niamey.

She said the violence began around 1200 GMT.

"There is a coup attempt" going on, a senior French official told AFP, speaking on condition of anonymity.

"All I can say is that it would appear that Tandja is not in a good position," he said.

Another witness said shooting had broken out around the presidential palace.

"The shots were directed at the president's office," said the witness, speaking from his workplace situated opposite the complex.

Sporadic shooting continued an hour later, an AFP correspondent who approached the palace said. Soldiers had deployed in the area and nearby streets were deserted.

The correspondent said he saw an armoured personnel carrier driven out of the palace gates before he was ordered away by a soldier.

After dissolving parliament, Tandja went on to stage parliamentary elections in October, which led the 15-nation West African regional bloc ECOWAS to suspend Niger's membership. The European Union suspended development aid and the United States imposed sanctions.

ECOWAS leaders meeting in Abuja on Tuesday urged all involved in the interim adminstration, including the military "not to put themselves up as candidates in the next elections".

Talks between Niger's government and the opposition to end the political standoff were suspended last week, having repeatedly stalled since they began on December 21.

ECOWAS mediator Abdulsalami Abubakar is chairing the talks, aimed at collecting views on a nine-point roadmap presented to the parties in January, that proposed keeping Tandja in power during a transition period led by a "government of national reconciliation."