PARIS — Former President Nicolas Sarkozy of France was placed under formal investigation on Wednesday as part of an inquiry into whether his 2007 election campaign received illegal financial support from the Libyan government of Col. Muammar el-Qaddafi.

Mr. Sarkozy, 63, faces charges of passive corruption, illegal campaign financing and misappropriation of Libyan public funds after a second day of questioning by the police in Nanterre, northwest of Paris, according to a spokeswoman for the French judiciary who spoke on the condition of anonymity in line with department policy.

The charge of passive corruption applies to people suspected of receiving money or favors.

The official said Mr. Sarkozy had denied any wrongdoing and had been placed under judicial control after his release from police custody. Under French law, judicial control can entail any number of obligations for a suspect for the duration of an investigation, including travel restrictions, but the official did not provide details.

The charges are a serious step up in the investigation, which was opened in 2013 and has slowly untangled a complex web of political and financial ties involving Mr. Sarkozy’s advisers, officials who were part of Colonel Qaddafi’s government before he was ousted and killed in 2011 and middle men who played a murky role as intermediaries between the two.