French ex-President Nicolas Sarkozy has been detained for questioning over alleged influence peddling.
The decision to detain him at Nanterre, near Paris, is an unprecedented step against a former president.
Sarkozy’s lawyer was questioned on Monday on suspicion of seeking inside information about a case against the former leader.
The latest developments are seen as a blow to Sarkozy’s attempts to challenge for the presidency in 2017.
Investigators are trying to find out whether Sarkozy, who was president from 2007 to 2012, had promised a prestigious role in Monaco to a high-ranking judge in exchange for information.
Gilbert Azibert, one of the most senior judges at the court of appeal, was also called in for questioning on Monday. Another judge, Patrick Sassoust, was also held.
The decision to detain Sarkozy is thought to be the first time a French former head of state has been held in police custody.
His predecessor, Jacques Chirac, was however given a suspended prison sentence in 2011 for embezzlement and breach of trust while he was mayor of Paris.
Investigators will be able to hold Sarkozy for an initial period of 24 hours but can extend custody for another day.