"The court is about to rule [on whether he should be held]", Nice's Public Prosecutor Jean-Michel Pretre told Sputnik.
French police have detained a Russian lawmaker and tycoon in southern France as part of a probe into suspected laundering of tax fraud proceeds, a French prosecutor said Tuesday. Russia's diplomatic mission in France is also engaged in this work.
"The status of a senator and the fact that he [Kerimov] is a Russian citizen are a guarantee that we will certainly make every effort to defend his legal interests", the spokesman stressed.
The spokesman argued that Mr Kerimov had diplomatic immunity, which puts officials from overseas above the law of the country in which they are working.
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.
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A regular visitor to France's Cote d'Azur, he has owned stakes at various times in Russian energy, banking and mining giants such as Gazprom, Sberbank and potash producer Uralkali.
Until a year ago, Kerimov owned Russia's Anzhi Makhachkala football club, the BBC added.
Kerimov, who is among the richest people in Russian Federation, was snatched by French law enforcement after arriving in Nice on Monday night.
In 2006, he crashed his Ferrari while speeding along Nice's seafront, sustaining severe burns.