An appeal court in southern France ordered billionaire Russian businessman and senator Suleyman Kerimov to post bail of 40 million euros ($47 million) on Wednesday pending a tax fraud investigation.
Kerimov, 51, was arrested in late November in the city of Nice over suspected tax evasion related to the purchase of luxury properties on the French Riviera, provoking an angry reaction from Moscow.
He posted bail of five million euros and handed over his passport after he was charged with tax fraud on November 23, but prosecutors lodged an appeal for a heftier bond.
The oligarch, who has denied any wrongdoing, left the appeal court in Aix-en-Provence flanked by bodyguards without speaking to reporters.
The case has signalled French prosecutors' willingness to pursue alleged money laundering and tax evasion in the top-end property market in the south of France which has long been a favourite destination for the rich and famous.
Nice prosecutor Jean-Michel Pretre said Monday that between 500 million and 750 million euros in "secret money" was involved.
Investigators suspect that a shell company used huge amounts of undeclared cash, drawn from accounts in Switzerland and Monaco, in the purchases of five luxury villas on the exclusive Cap d'Antibes peninsula on Kerimov's behalf.
Some of the transactions were thought to exceed 100 million euros. One property has since been sold, while authorities have seized the other four.
The court also released estate agent Irina Sadikova, the only suspect detained in the affair who was held for two weeks. She was ordered to pay bail of 300,000 euros
She has admitted to earning a two-million-euro commission for the sale of a villa and stashing the money in Switzerland.
Kerimov's French manager Cedric Faugeroux has meanwhile been placed under legal supervision after posting a bond of 800,000 euros.
Kerimov's detention prompted the Russian government to summon France's deputy ambassador.
Listed by Forbes magazine as Russia's 21st richest person with an estimated net worth of $6.3 billion, Kerimov made his transition from rags to riches during the privatisations that followed the break-up of the Soviet Union.
Known as one of Russia's most eligible bachelors, the flamboyant but media-shy Kerimov has hired the likes of Beyonce to entertain friends in Cap d'Antibes, even in the midst of the 2008 global financial crisis -- in which he lost billions.
Originally from Russia's North Caucasus region of Dagestan where he began his working life at a Soviet transistor factory, Kerimov has owned stakes at various times in Russian energy, banking and mining giants such as Gazprom, Sberbank and potash producer Uralkali.
- Family gold -
The billionaire previously controlled Dagestan's Anzhi Makhachkala football club, which at one point topped the Russian league when he poured millions into buying players like Roberto Carlos and Samuel Eto'o.
But after losing a significant part of his fortune, he sold most of his shares in the club.
His family now controls Russia's largest gold producer, Polyus.
Kerimov was once a member of the ultra-nationalist Liberal Democratic Party, which he left in 2007 to join the ruling United Russia.
Since 2008, he has represented Dagestan as a senator in the Federation Council, the upper house of Russia's parliament.
In 2006, he crashed his Ferrari Enzo while speeding along Nice's seafront, sustaining severe burns.