Sarkozy, who spent nearly a day in custody Tuesday answering questions about his 2007 presidential campaign, said on TF1 TV and Europe-1 radio that he was "profoundly shocked" over his 16-hour detention.
"Is it normal that I should be in custody for so long?" Sarkozy asked, squinting intensely at an interviewer. He said his detention was motivated out of "a desire to humiliate me. A part of the justice system is being used for political purposes. In our country ... there are things that are in the process of being organized. The French need to know them, and in their conscience, and freely, need to judge what's happening."
Le Monde newspaper has reported that the questioning centers on whether Sarkozy and his lawyers were informed about an investigation into the Libyan case by Magistrate Gilbert Azibert in exchange for promises that were never fulfilled for him to receive a post in Monaco.
"Azibert did not get a post in Monaco," Sarkozy said. "There has been no move in favor of Monsieur Azibert."
Earlier, Prime Minister Manuel Valls said the investigation was being carried out independently of the Socialist government. His boss, Socialist President Francois Hollande, defeated Sarkozy in the presidential race in 2012.
"This situation is serious. The facts are serious," Valls told BFM TV. "But as head of the government, I'm asking that we remember the independence of the justice system, which must carry out its work serenely. No one is above the law is the second principle. And thirdly, an important reminder, there is the presumption of innocence."
Sarkozy is accused of tapping political allies to gain intelligence on a flurry of probes linked to campaign finance. He has vigorously denied the claims, and insisted Wednesday that he has "never betrayed trust" of the French people.
Sarkozy has drifted out of the political arena, but polls show he's still popular among his fellow conservatives.
His personal lawyer, Thierry Herzog, and Azibert were also questioned in the probe. Lawyers for those two men said they were handed preliminary charges of influence trafficking.
Jean Garrigues, a political historian at the University of Orleans and Paris' Sorbonne university, said the case amounts to "yet another thing to erode the image of the political class, because it gives the image of an all-powerful group that believes itself to be above the law."
After further investigation, judges will determine whether to hold a trial.
Sylvie Corbet and Lori Hinnant contributed to this report.