Omar Bongo's relations with Paris have deteriorated in recent years
French authorities have frozen Gabon President Omar Bongo's bank accounts.
The move comes after a Bordeaux court ordered President Bongo to return a payment made to him to release a jailed French businessman, Rene Cardona.
The BBC's Charles Mayard in Paris says it is the first time French authorities have frozen the accounts of an acting head of state.
Mr Bongo, Africa's longest-serving leader, is thought to have more than $4m (£2.8m) in French bank accounts.
Mr Cardona was freed after his son paid more than $580,000 (£400,000) into 72-year-old Mr Bongo's account, a court heard.
In September, a court ruled that payment had been illegal.
That verdict was confirmed on appeal on Monday.
Jean-Philippe Le Bail, a lawyer for the jailed businessman's son, told AFP news agency on Thursday: "The accounts held by Omar Bongo in two French banks have been seized."
Rene Cardona was imprisoned in 1996 after a business dispute with Mr Bongo, to whom he had sold a shipping and fishing firm.
Mr Bongo's lawyer, Francois Meyer, told the BBC that the Gabonese president refuses to repay the money. Mr Meyer alleged that Mr Cardona still owes the Gabonese president money from the sale of the firm.
Mr Meyer added that the $580,000 was paid to Mr Bongo in connection with the sale of the firm and not for the release of Mr Cardona.
But this was denied by Mr Cardona.
"It's the amount my son was forced to pay to secure my release," he told the BBC.
As part of the row over the firm's ownership, a court in the Gabonese capital Libreville had ordered Mr Cardona to pay Mr Bongo $1,148,000, according to Mr Meyer.
"That Libreville court order was made in my absence four or five years ago. And it was rejected by the Bordeaux court of appeal," Mr Cardona said.
Mr Bongo has been a close associate of a string of French leaders but his relations with Paris have deteriorated in recent years amid legal challenges by anti-corruption activists.