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 the Russian government.
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.
Nice prosecutor Jean-Michel Pretre said Monday that between 500 million and 750 million euros in "secret money" was involved.
Investigators suspect that a front man 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 on bail of 300,000 euros estate agent Irina Sadikova, the only suspect detained in the affair.
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 and angry Russian MPs passed a resolution branding the arrest a violation of the 1961 Vienna Convention on Diplomatic Relations, urging Moscow to press for his release.
Listed by Forbes magazine as Russia's 21st richest person with an estimated net worth of $6.3 billion, Kerimov made his fortune during the privatisations that followed the break-up of the Soviet Union.
Originally from Russia's North Caucasus region of Dagestan, 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 party Liberal Democratic Party, which he left in 2007 to join the ruling United Russia party.
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 while speeding along Nice's seafront, sustaining severe burns.