France's ex-president Nicolas Sarkozy appeared before a judge Thursday to respond to charges that his 2007 electoral campaign was financed with funds secured illegally from France's richest woman.

Sarkozy arrived for the hearing in a dark grey Renault minivan just before 9:15 in the morning, an AFP correspondent said.

In a case that could wreck the 57-year-old's hopes of a political comeback, Sarkozy is suspected of taking financial advantage of elderly L'Oréal heiress Liliane Bettencourt at a time when she was too frail to fully understand what she was doing.

Sarkozy's appearance comes with his right-wing party, the Union for a Popular Movement, in turmoil after the battle to replace him degenerated into mud-slinging and both contenders claimed victory.

Examining magistrate Jean-Michel Gentil is expected to spend most of the day quizzing Sarkozy about how he obtained funding from Bettencourt.

Judicial sources have told AFP that Sarkozy could be formally indicted on a charge of taking advantage of someone in a position of weakness, although the magistrate also has the option of interrogating him as a witness under caution.

Bettencourt is now 90 and has been in poor health since 2006.

The allegation against Sarkozy is two-fold: that the money obtained from her took his campaign financing over legal limits and that it had been secured without her full knowledge or consent.

This latter claim was made by Bettencourt's former accountant, Claire Thibout in 2010.

She told police that she had handed 150,000 euros ($193,000) in cash to Bettencourt's right-hand man, Patrice de Maistre, on the understanding it was to be passed on to Sarkozy's campaign treasurer, Éric Woerth.

Maistre withdrew a total of 4 million euros in cash from Bettencourt's Swiss bank account in seven installments between 2007 and 2009.

Investigators suspect some or all of the money could have found its way to Sarkozy or his party.

In July, the examining magistrate ordered the seizure of Sarkozy's diaries in order to establish what he was doing around the time the cash was being moved.

Claude Guéant, a close ally of Sarkozy who served as his interior minister, said the courts needed to show why his questioning was necessary.

"I would like to be absolutely convinced that this hearing is essential," he told RTL radio, insisting there was no chance of illegal campaign financing because of "extremely rigorous" controls put in place.

French authorities confirmed this week they have also opened a preliminary investigation over the management of opinion polls carried out during Sarkozy's 2007-12 term as president.

AFP