Army officers have appeared on national television in Gabon to say they have taken power.
They said they were annulling the results of Saturday’s election, in which President Ali Bongo was declared the winner.
The electoral commission said Mr Bongo had won just under two-thirds of the votes in an election the opposition argued was fraudulent.
His overthrow would end his family’s 53-year hold on power in Gabon.
Twelve soldiers appeared on television on Wednesday, announcing they were cancelling the results of the election and dissolving “all the institutions of the republic”.
They also said the country’s borders had been closed “until further notice”.
One of the soldiers said on TV channel Gabon 24: “We have decided to defend peace by putting an end to the current regime.”
This, he added, was down to “irresponsible, unpredictable governance resulting in a continuing deterioration in social cohesion that risks leading the country into chaos”.