Former French President Nicolas Sarkozy was placed under formal investigation early Wednesday in connection with suspected corruption and influence peddling, French media said.
He appeared before a court overnight after a day of questioning in a Paris suburb, CNN's French affiliate BFMTV reported.
He is reportedly the first French president to be held in police custody in connection with an investigation.
Sarkozy, speaking to French broadcasters TF1 and Europe 1, said Wednesday he was "deeply shocked."
In the taped joint interview, Sarkozy said that there is a "willingness to humiliate" him, and that he "never committed any act contrary to republican principles or the rule of law."
The former President added that he "is not asking for any privilege" and that he "is not a man who escapes from his responsibilities."
Sarkozy's lawyer, Thierry Herzog, and a high-ranking magistrate, Gilbert Azibert, were also placed under formal investigation Tuesday, BFMTV said. They were called in for questioning Monday, along with another magistrate who was not brought before a judge.
Prime Minister Manuel Valls told BFMTV Wednesday that Sarkozy faced a "serious situation" and "serious facts."
"No one is above the law, but it is important to remember that the presumption of innocence applies to everyone," he said.
Investigators who have been looking into Sarkozy's campaign financing are trying to establish whether the former President obtained confidential information on legal cases concerning him from magistrates in exchange for the offer of a prestigious post, BFMTV reported.
Sarkozy, who led the country from 2007 to 2012, lost in the 2012 presidential election to Socialist rival Francois Hollande.
In recent months, speculation has grown that he might be positioning himself for a political comeback at the head of his center-right party, the UMP.
The latest investigation into his actions could prove damaging to his ambitions even if no charge follows.
Prime Minister Valls, in his interview with BFMTV, rejected any suggestion that the investigation was politically motivated, insisting that judges work entirely independently.
It's not the authorities who have asked these judges to investigate, he said.
The offense of "active corruption" carries a penalty of up to 10 years in prison and a fine, under the French penal code. Influence peddling is punishable by up to five years in prison and a 500,000 euro ($683,000) fine.
Bordeaux Mayor Alain Juppe, a UMP politician who formerly served as prime minister and foreign minister, said via Twitter that he was thinking of Sarkozy in a spirit of friendship.
"He is, of course, presumed innocent. His defense will demonstrate his innocence, I hope," he posted.