Syrian leader Bashar al-Assad's uncle Rifaat did not use illegally acquired funds to build a real estate empire in France, his son said Thursday.

Paris prosecutors on Monday launched a preliminary investigation into the wealth of Rifaat al-Assad, 76, following a criminal complaint filed on September 13 by anti-corruption groups Sherpa and Transparency International.

The complaint says the money was obtained through corruption and embezzlement, basically using cash siphoned out of Syria.

Rifaat al-Assad's son Siwar al-Assad told a press conference that the money for the "legitimately acquired assets" did not come from Syria.

He said when Rifaat al-Assad came to France in 1984 after breaking with the government of his brother Hafez, he "received the financial backing of his friends who supported him then, who support him now and who will support him tomorrow."

"It's not Syrian public funds," Siwar al-Assad said.

French media have reported that Rifaat al-Assad's holdings include a mansion and several dozen apartments in Paris, with newspaper Le Monde estimating the total value of his estate in France at 160 million euros ($215 million).

Cedric Anthony, who oversees Rifaat al-Assad's real estate, said the donors included "governments, kingdoms and individuals."

Anthony confirmed that a mansion belonging to Rifaat al-Assad on Paris's ultra-chic Avenue Foch was on the market for 90 million euros.

Rifaat al-Assad's lawyer said his properties included 14 apartments in the French capital's wealthy 16th district as well as land and a building in the city of Lyon.