Patrice de Maistre, who had already been placed under investigation in December over allegations of fraud, conspiracy, money laundering and possession of stolen goods, was previously alleged to have made a 150,000 euro ($198,000) payment to former French budget minister Eric Woerth on Bettencourt's behalf.

De Maistre's imprisonment pending trial was the latest twist in a more than four-year battle over Bettencourt's fortune, estimated by Forbes magazine at $24 billion.

Woerth in February was placed under judicial investigation for illicit party financing related to cash he was alleged to have received from Bettencourt to fund French President Nicolas Sarkozy's 2007 presidential campaign.

Last October, Bettencourt's daughter Francoise Meyers-Bettencourt won control over the 89 year old's business affairs on the basis of a medical examination which concluded she was suffering from a form of dementia.

De Maistre, who formerly helped manage the fortune of Bettencourt, France's wealthiest woman, was questioned again on Friday by Judge Jean-Michel Gentil after the emergence of "new evidence" which came to light "after additional investigations," prosecutors said in a statement.

"This evidence involves in part the collection by Patrice de Maistre of 2.96 million euros as part of an agreement between the Eugenia firm, of which he was a manager, and Liliane Bettencourt, at the time in a situation of vulnerability," prosecutors said.

De Maistre's firm Eugenia was also alleged to have improperly billed Clymene, the company owned by Bettencourt to manage her wealth, the prosecutors said.

In February, Bettencourt was replaced on L'Oreal's board by her 25-year-old grandson Jean-Victor Meyers.

($1 = 0.7579 euros)

(Reporting by Claude Canellas; Writing by Christian Plumb; Editing by David Holmes)

• A Permanent Economic Emergency