Paris prosecutors opened a preliminary investigation Monday into the assets of Syrian President Bashar al-Assad\'s uncle, whom anti-corruption groups accuse of illegally obtaining a vast fortune and property empire. A judicial source told AFP the investigation had been opened into Rifaat al-Assad, the brother of Bashar al-Assad\'s father Hafez, after a criminal complaint filed on September 13. The complaint, by anti-corruption groups Sherpa and Transparency International, alleges the 76-year-old illegally acquired \"extraordinary wealth\" in France through corrupt schemes and embezzlement. Once a stalwart of the Syrian authorities, Rifaat al-Assad broke with his brother\'s government in 1984 and reportedly has no links with the current regime, which is fighting in a civil conflict that has left more than 110,000 dead since it began in March 2011. Before splitting from the regime, Rifaat al-Assad was accused of being responsible for the deaths of thousands during the crushing of a Sunni Islamist uprising in 1982. The massacre in the town of Hama, by troops allegedly under Rifaat al-Assad\'s command, left between 10,000 and 25,000 dead. Rifaat al-Assad has denied any involvement and in 2011 dismissed allegations he was behind the killings as \"a myth.\" The criminal complaint accuses Rifaat al-Assad of acquiring wealth \"in the billions of euros\" through corruption, embezzlement of public funds, misuse of corporate assets and other crimes, noting that he had \"no known professional activity.\" The head of Sherpa, William Bourdon, welcomed the prosecutors\' decision as a \"first step\" but said a full probe by investigating magistrates needed to be launched. \"It is obvious that only an examining magistrate has the necessary authority to deal with offences of such a complex and international nature,\" he told AFP, adding that a magistrate would also have more power to seize assets. Rifaat al-Assad\'s lawyer, Marcel Ceccaldi, condemned the launching of the investigation so many years after his client settled in the country as evidence of \"French arrogance.\" \"This is a man who has been here since 1984, who purchased these assets between 1984 and 1986,\" he said, noting that Rifaat al-Assad had also been granted the Legion d\'Honneur -- France\'s highest honour -- by then-president Francois Mitterrand in 1986. 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). Le Monde reported earlier this year that the potential sale of one of his properties -- a mansion on the prestigious Avenue Foch -- fell through after potential Russian buyers offered only 70 million euros. Once considered a possible successor to his brother, Rifaat al-Assad fled to France after being placed under house arrest following a failed coup attempt. His estrangement from the regime means he has not been affected by the freezing of assets and travel restrictions imposed by the European Union against Bashar al-Assad\'s inner circle. Rifaat\'s son, Siwar al-Assad, told France Info radio earlier that the family\'s wealth was legitimate and promised to cooperate with any investigation. He said that after settling in France his father had received funds from \"states, leaders and friends abroad.\" \"We are utterly transparent in our investments, nothing was done in secret, the origins of our funds were completely legal,\" he said.