The former right-hand man of French ex-President Nicolas Sarkozy was arrested on Tuesday for questioning about alleged misuse of public funds when he served the conservative leader at the Interior Ministry, a judicial source said.
Claude Gueant, interior minister until May last year and Sarkozy's chief of staff between 2002 and 2011, was put under preliminary investigation in June after police found evidence of cash purchases worth some 20,000 euros ($27,500) in a search of his home.
Gueant has said the money was drawn from a cash fund used to finance police informers and surveillance operations when Sarkozy was interior minister prior to his election as president in 2007.
A preliminary investigation means police can continue to gather evidence with a view to pressing formal charges but it does not automatically lead to an indictment.
Michel Gaudin, another close Sarkozy aide and former head of police, was also being questioned about alleged corruption and tax evasion at the headquarters of the judicial police in the Paris suburb of Nanterre.
The high-profile arrests targeted two former close allies amid media reports that Sarkozy is preparing to run for re-election in 2017.
Sarkozy himself was cleared in October in an investigation into suspicions that he had manipulated France's richest woman into financing his 2007 campaign, removing an obstacle to his return to national politics.