The son of Libyan leader Muammar Gaddafi has alleged that his country helped finance Nicolas Sarkozy's 2007 presidential election campaign.
"We funded it and we have all the details and are ready to reveal everything," Saif al-Islam said.
His remarks to the Euronews TV channel came days after Libyan state TV reported a "grave secret" that would bring about Mr Sarkozy's downfall.
The Elysee Palace has denied Mr Sarkozy benefited from any funding from Libya.
"We deny it, quite evidently," a spokesman told Le Monde's website.
Libya had threatened to reveal more about the "grave secret" if France went ahead with its decision to recognise the rebel Transitional National Council as the legitimate representative of the Libyan people.
France has been at the forefront of efforts to secure a no-fly zone to halt the advance of Col Gaddafi's forces against Libyan rebels.
In the interview, Saif al-Islam referred to Mr Sarkozy as "this clown" and said he was given assistance so that he could help the Libyan people.
"But he's disappointed us," he said. "Give us back our money. We have all the bank details and documents for the transfer operations and we will make everything public soon."
Col Gaddafi was greeted by Mr Sarkozy when he visited Paris in December 2007, months after the French leader's ex-wife Cecilia had flown to Tripoli to help secure the release of six Bulgarian doctors.
In the Euronews interview, Col Gaddafi's son said military operations against the rebels were "finished" and everything would be over within 48 hours.