Investigators are examining claims that Gaddafi's regime secretly gave the politician €50 million overall for his campaign.
The sum would be more than double the legal campaign funding limit at the time — €21m. In addition, the alleged payments would violate French rules against foreign financing and requiring that the source of campaign funds be declared.
His lawyer, Thierry Herzog, did not respond to requests for comment.
Sarkozy's former top aide, the ex-minister Brice Hortefeux, was also questioned, but not detained.
He said on Twitter that the details he gave investigators "should help put an end to a series of mistakes and lies."
The investigation got a boost when French-Lebanese businessman Ziad Takieddine told the online investigative site Mediapart in 2016 that he delivered suitcases from Libya containing €5m in cash to Sarkozy and his former chief of staff, Claude Gueant.
Takieddine repeated his allegations during a live interview with France's BFM TV today. He claimed he personally handed a suitcase containing €2m in cash to Sarkozy at the then-candidate's apartment and another suitcase with €1.5m to Sarkozy and a close aide at the French Interior Ministry. Sarkozy was interior minister at the time.
Takieddine alleged he gave a third suitcase with €1.5m in cash to the aide alone. He said the money was not meant to finance Sarkozy's presidential campaign in 2007, but to honour contracts between France and Libya.
"He's a real liar," Takieddine said of Sarkozy.
-AP