NICE/MOSCOW (Reuters) - A French judge put Russian businessman and lawmaker Suleiman Kerimov, whose interests the Kremlin has pledged to defend, under formal investigation on Wednesday after his arrest linked to a French tax evasion case, the prosecutor said. The investigation, a step that often but not always leads to a trial in the French legal system, was opened on suspicion of aggravated laundering of tax fraud proceeds, a crime that carries a prison sentence of up to 10 years. The judge decided that Kerimov could be released from detention but had to turn in his passport and could not leave the Alpes-Maritime county Nice is in. He was also ordered to post a bail of five million euros ($5.9 million) and to check in with police several times per week. The Kremlin said earlier that it would spare no effort to defend the rights of Kerimov, a 51-year-old billionaire who was arrested Monday night in the French Riviera resort city of Nice. Shares in Polyus, Russia s biggest gold producer which is controlled by Kerimov s family, fell on the news of his detention.  We will do everything in our power to protect his lawful interests,  Kremlin spokesman Dmitry Peskov told a conference call with reporters.  Intensive work is now being undertaken by the foreign ministry.  The prosecution requested that Kerimov be kept in custody and a decision by a judge was expected soon. A second person was also put under formal investigation. A representative for Kerimov in the upper house of Russia s parliament, where he sits as a lawmaker, declined to comment on the case on Wednesday when contacted by Reuters. Polyus also declined to comment. Russia s state-run Rossiya 24 TV station, citing an unnamed source, reported that Kerimov had denied any guilt. It was not immediately clear if a lawyer had been hired to represent Kerimov in France. In the lower house of parliament, lawmaker Rizvan Kurbanov asked the Russian foreign ministry to make representations on Kerimov s behalf with the French authorities.  We have still not received from the French authorities any explanation of the reasons for the detention of our colleague,  Kurbanov told parliament.  All this testifies to an unprecedented demarche by the French,  he said, adding that he hoped the Russian foreign ministry would issue a formal protest. Shares in Polyus fell more than 3 percent in early trade in Moscow on Wednesday but then recovered some ground to close down 1.25 percent. Originally from the mainly Muslim Russian region of Dagestan, Kerimov built his lucrative natural resources business through a combination of debt, an appetite for risk, and political connections. He owned top flight soccer club Anzhi Makhachkala until he sold it in 2016. Kerimov s fortune peaked at $17.5 billion in 2008 before slumping to just $3 billion in 2009, according to Forbes magazine, due to so-called margin calls on his assets triggered by the 2007-2009 global financial crisis. In March this year, Russian President Vladimir Putin signed a decree giving Kerimov the state award  For Services to the Fatherland, second class  for his contribution to Russian parliamentary life. French police arrested Kerimov at Nice airport on Monday evening. A French judicial source said the investigation centered on the purchase of several luxury residences on the French Riviera via shell companies, something that could have enabled Kerimov to reduce taxes owed to the French state. ($1 = 0.8465 euros) 