"The United States is deeply concerned about today's developments in Niger," the White House said in a statement. "We specifically urge elements of the presidential guard to release President Bazoum from detention and refrain from violence."

The West African bloc ECOWAS, the African Union and the European Union condemned what they called an "attempted coup d'etat," a description echoed by a source close to Bazoum who also predicted the bid would fail.

A close ally of France, Bazoum was elected in 2021, taking the helm of a country mired in poverty and burdened by a history of chronic instability.

Members of the elite Presidential Guard on Wednesday morning sealed off access to the president's residence and offices, and after talks broke down "refused to release the president," another presidential source said.

"The army has given them an ultimatum," said the source, who spoke on condition of anonymity.

In a message on Twitter, which is being rebranded as X, the president's office said "elements of the Presidential Guard (PG) had a fit of temper... (and) tried unsuccessfully to gain the support of the national armed forces and the national guard."

"The army and national guard are ready to attack the elements of the PG who are involved in this fit of temper if they do not return to a better disposition," the presidency said.

"The president and his family are well," it added.

The reason for the guards' anger was not disclosed.

Access was blocked off to the presidential complex in Niamey, although there was no abnormal military deployment or sounds of gunfire in the area, and traffic was normal, an AFP journalist saw.

The Economic Community of West African States (ECOWAS) and AU issued separate statements condemning an "attempted coup d'Etat".

ECOWAS called for Bazoum's immediate and unconditional release and warned that all those involved would be held responsible for his safety.

The source close to Bazoum, speaking on condition of anonymity, said that the attempt to seize power was "doomed to fail."

The EU said it "associates itself" with the ECOWAS statement, with foreign policy chief Josep Borrell posting online: "The EU condemns any attempt to destabilise democracy and threaten the stability of Niger".