Suleiman Kerimov watches a soccer in Makhachkala December 2, 2012. REUTERS/Sergei Rasulov/ NewsTeam

NICE, France (Reuters) - Billionaire Russian businessman Suleiman Kerimov was put under formal investigation on Wednesday in Nice in southern France on suspicions of laundering tax fraud proceeds, Nice prosecutor Jean-Michel Pretre said.

Under France’s legal system, being formally placed under investigation often - but not always - leads to a person being sent to trial.

French police arrested the 51-year-old businessman and lawmaker at Nice airport on Monday evening in connection with a tax evasion case.

The prosecution requested that Kerimov be kept in custody and a decision by a judge was due in the night from Wednesday to Thursday.

Earlier a French judicial source said investigators were focussing 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.