Bettencourt's former accountant Claire Thibout was said
to have told police she was involved in transferring 150,000 euros to Mr Sarkozy's presidential campaign in 2007, above the set limit of 7,500 euros for donations to political parties in France.
Mr Sarkozy has dismissed the claim as a "smear". Campaign treasurer Eric Woerth has also denied the claim and is suing for slander.
Ms Thibout reportedly said the money was to be handed over to Mr Woerth, who is currently both treasurer for Mr Sarkozy's UMP party and also France's labour minister.
assumed office as French president on 16 May 2007 after defeating the then Socialist candidate Segolen Royal 10 days earlier.Before his presidency, he was leader of the Union for a Popular Movement
, the French conservative party, elected with 85 percent of the vote.
His political career
began when he was 23, when he became a city councillor in Neuilly-sur-Seine
and went on in 1988 to be the youngest elected mayor of that town, after the death of the incumbent mayor.