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Guy-Bertrand Mapangou told the BBC that four of the rebels had been arrested by the authorities while a fifth is on the run.
Junior officers claimed they seized power “to restore democracy” in oil-rich Gabon, where the ailing leader’s family has ruled for 50 years.
Tanks and armed vehicles could be seen in the capital Libreville.
The soldiers took control of the national radio station at 04:30 local time (03:30 GMT) to read a short statement announcing a “National Restoration Council”.
Current leader, Ali Bongo, succeeded his father, Omar Bongo, as president in 2009.
He narrowly won re-election in 2016 in a poll marred by violence and accusations of fraud.
The coup attempt came as a huge surprise as the army had always been seen as loyal to the Bongo family.
Reports say that the army is dominated by the presidential guard who mostly come from Mr Bongo’s home region.
