French prosecutors have launched an investigation into alleged embezzlement by two African leaders.
President Bongo is alleged to have embezzled funds for property
The corruption investigation was launched this week after complaints by three agencies in March that property had been bought with stolen funds.
It included a Paris mansion owned by Gabon President Omar Bongo Ondimba and his family and a luxury townhouse owned by Congo's leader Denis Sassou Nguesso.
Neither Mr Bongo nor Mr Sassou Nguesso have answered the allegations.
Several other properties are believed to be involved in the investigation.
They include flats linked to Mr Nguesso's family in Paris's Foch Avenue, in Parisian suburbs such as Courbevoie and Velizy, and in expensive areas in the south of France such as the Cote d'Azur, the BBC's Catherine Zemmouri in Paris says.
The three groups making claims against the two leaders were Survie (Survival), which has criticised France's support of African dictators in the past, an international network of legal experts called Sherpa and the Federation of Congolese from the Diaspora, AFP news agency said.
"The properties never belong directly to presidents themselves but instead to their daughters, sons, nephews or [are] registered to properties companies," Benjamin Mutsila president of Congolese Diaspora told the BBC.
"It is not a president's salary that could have generated the considerable resources needed to acquire such property," said lawyer William Bourdon, president of the Sherpa group, quoted by AFP.
President Sassou Nguesso is implicated in the probe, critics say
"We hope the French judge will seize all this properties, which can have only been bought with oil incomes and sell it in order to send the money back to Congo and to Gabon," Survie said in a statement.
"Citizens live in poor conditions without enough hospitals, schools and public infrastructure."
Mr Bongo, 71 and Africa's longest-serving head of state, won re-election last year for another seven-year term.
He has ruled the oil-rich country since 1967.
Mr Sassou Nguesso, 63, ruled Congo from 1979 to 1992, and then returned to lead the country after a coup in 1997.