French President Francois Hollande on Thursday said respect for judges was sacrosanct after backers of his predecessor questioned the credentials of a magistrate who charged Nicolas Sarkozy in a corruption probe.
Judge Jean-Michel Gentil created a storm last week by placing Sarkozy under formal investigation for alleged financial abuse of the country's richest woman, L'Oreal heiress Liliane Bettencourt.
Gentil, who has received death threats, has been accused of being politically motivated by a number of Sarkozy supporters as well as by the former president's own lawyer, Thierry Herzog.
"I cannot accept that a judge is put under suspicion," Hollande said in a television interview on France 2 channel.
"In no way can the credibility of a judge -- and this applies to all cases -- be put into question," he said, noting that Sarkozy was "presumed innocent" until found otherwise.
Henri Guaino, a lawmaker and former special adviser to Sarkozy who said earlier this week that Gentil's conduct had "dishonoured justice", was standing by his comments on Thursday.
Sarkozy denies allegations he accepted cash-stuffed envelopes from Bettencourt to fund his successful 2007 campaign. The ageing heiress has suffered from dementia since 2006.
If convicted of taking advantage of her, Sarkozy faces up to three years in jail, a fine of 375,000 euros ($480,000), and a five-year ban from public office.