AU chief Moussa Faki Mahamat, in a tweet, said his organisation "strongly condemns the coup attempt" in Gabon.

"I reaffirm the AU's total rejection of all unconstitutional change of power," said Faki, who is chairman of the AU commission.

Separately, France, which ruled Gabon from 1885 until independence in 1960, said it condemned "any extra-constitutional attempt at regime change."

"The stability of Gabon can only be assured by strict adherence to the provisions of the constitution," foreign ministry spokeswoman Agnes von der Muhll said in Paris.

The ministry also advised French nationals in the capital Libreville -- 8,900 of whom have registered with the French consulate -- to "avoid moving around" in the capital for time being.

Earlier, a group of soldiers took over the headquarters of the state broadcaster at dawn and issued a statement calling on the public to "rise up."

But within hours, the government said the situation was under control and four of the five rebels had been arrested while a fifth was on the run.

The upheaval comes as President Ali Bongo is in Morocco after suffering a stroke while abroad.

The 59-year-old, scion of a family that has ruled Gabon for more than half a century, has not been in the country since October.

In his absence, the Constitutional Court transferred part of the powers of the president to the prime minister and the vice president.

The statement read out by the rebels on Monday attacked the arrangement as "illegitimate and illegal."