French prosecutors said Friday that they had slapped criminal conspiracy charges on former president Nicolas Sarkozy over claims he used Libyan cash for his 2007 election campaign.

The charge for "membership in a criminal conspiracy" was brought on Monday, the prosecutors told AFP. It adds to charges lodged in 2018 of "passive corruption," "benefitting from embezzled public funds" and "illegal campaign financing" for which Sarkozy already faces trial.

The latest charge, which can be appealed under French law, came after prosecutors interviewed the rightwing conservative for more than 40 hours over four days. Prosecutors suspect that Sarkozy and his associates received dozens of millions of euros from the regime of former strongman Moamer Kadhafi to help finance his election bid.

'Innocence tarnished'

Sarkozy, who was president from 2007 to 2012, has denied any wrongdoing, saying on his Facebook page Friday that his "innocence has been tarnished" by the charges, without "even the slightest proof."

He said that during the questioning "I answered every question I was asked without ever being put in difficulty."

Last month, a Paris appeals court threw out Sarkozy's bid to have the investigation dismissed, making a trial more likely. Sarkozy, 65, denies the charges that were sparked by investigative website Mediapart in 2012, when it published a document purporting to show that Kadhafi agreed to give Sarkozy up to 50 million euros ($59 million at current rates).

In his defence Sarkozy -- who is himself a trained lawyer -- has claimed presidential immunity, and said there is no legal basis in France for prosecuting someone for misusing funds from a foreign country.

Judges are also investigating claims by a French-Lebanese businessman, Ziad Takieddine, who said he delivered suitcases carrying a total of five million euros from the Libyan regime to Sarkozy's chief of staff in 2006 and 2007.

After seven years of investigation efforts resulting in witness statements from Libyan officials, Kadhafi's secret service and from middlemen, prosecutors believe they can show that Sarkozy's campaign was indeed financed by Kadhafi.

But legal experts also question whether the charges hinge on circumstantial evidence rather than the sort of ironclad proof of Sarkozy's guilt that would ensure a conviction. Sarkozy's former ministers Claude Gueant and Eric Woerth are also charged in the case, which is not the only legal headache for the former rightwing president, who is no longer active in politics.

He has also been charged in two other cases, one relating to fake invoices devised to mask overspending on his failed 2012 re-election campaign, and another for alleged influence peddling.