NICE, France (Reuters) - Russian businessman and lawmaker Suleiman Kerimov was arrested by French police at Nice airport on Monday evening in connection with a tax evasion case, an official at the French prosecutor s office said on Tuesday. Kerimov is ranked by Forbes magazine as Russia s 21st wealthiest businessman, with a net worth of $6.3 billion. His family controls Russia s largest gold producer Polyus.   He is being held for questioning in a case related to laundering of tax fraud proceeds,  the official said. Representatives for Kerimov could not immediately be reached for comment. Polyus declined to comment. A source said the investigation centers on the purchase of several luxury residences on the French Riviera via shell companies, something that would have enabled Kerimov to reduce taxes owed to the French state. The source added Kerimov would be held in custody for at least another 24 hours. Russia s foreign ministry said in a statement carried by Interfax news agency that Kerimov held a diplomatic passport and had immunity. It said it had informed the French authorities.  Kerimov does have a diplomatic passport, but that does not protect him from prosecution,  the French official said. The French foreign ministry could not immediately confirm it had been in contact with Moscow. A French diplomatic source said immunity was given by governments to people on diplomatic lists or if they had been mandated with a specific mission in the country.    