Former French President Nicolas Sarkozy has been held in police custody for questioning over suspected influence-peddling, sources told Al Jazeera.
Sarkozy arrived early on Tuesday to be quizzed by investigators at their offices in Nanterre, west of Paris, after his lawyer was held for questioning on Monday.
"Mr. Sarkozy has been summoned to Nanterre and is being held for questioning," the source told Reuters.
Al Jazeera's Nadim Baba, reporting from Paris, said Sarkozy has not been charged with any wrongdoing.
The investigators are seeking to establish if the former president, with the help of his lawyer Thierry Herzog, attempted to pervert the course of justice.
They suspect Sarkozy, 59, sought to obtain inside information from one of the magistrates about the progress of another probe, and that he was tipped off that his mobile phone had been tapped by judges looking into the alleged financing of his 2007 election campaign by former Libyan dictator Muammar Gaddafi.
The case could be devastating for Sarkozy's hopes of a political comeback in time for the next presidential campaign in 2017.
Under French law, suspects in criminal cases can be held in custody for up to 48 hours before they must be charged or released.
Sarkozy is alleged to have been helped to victory in 2007 with up to $70 million provided by Gaddafi, and envelopes stuffed with cash from France's richest woman, L'Oreal heiress Liliane Bettencourt.
He dismissed the Gaddafi claims as ridiculous and was cleared last year of taking Bettencourt's money when she was too frail to know what she was doing.
His campaign treasurer is one of ten people awaiting trial in that case.
The Gaddafi investigation is ongoing. It was in connection with it that the judges last year obtained the unprecedented authorisation to tap the phones of a former president.
|Sarkozy charged with illegal fundraising
After four fruitless months they discovered Sarkozy had a secret phone registered under an assumed name and it was conversations with his lawyer Herzog, recorded on that device, which triggered the probe.
Leaked excerpts suggest Sarkozy got a friendly judge to try to influence the outcome of confidential legal deliberations related to the Bettencourt case in return for support securing a lucrative post in Monaco.
They also imply he had a mole in a senior position who tipped him off about a planned police raid on his offices.
Such interference in the judicial process is regarded as "influence peddling" in French law and carries a maximum prison sentence of 10 years.
Sarkozy has attacked the tapping of his phones as worthy of East Germany's notorious Stasi secret police.
The authorisation of recordings of lawyer-client conversations has also provoked misgivings within sections of France's legal establishment.
Separately, Sarkozy has recently been linked to a scandal over the funding of his campaign for re-election in 2012.
Sarkozy has been implicated in a number of other scandals which are still being investigated.
The most serious of these centres on an allegation that he helped organise kickbacks from a Pakistani arms deal to finance the 1995 presidential campaign of former premier Edouard Balladur.
He is also being probed over allegations that, while president, he used public funds to pay for party political research and handed out contracts for polling to a political crony.