PARIS — French prosecutors charged former president Nicolas Sarkozy with "criminal association" as part of an investigation into the financing of his 2007 presidential campaign, particularly its alleged ties to the government of then-Libyan dictator Moammar Gaddafi.

Although Sarkozy was charged in 2018 with corruption and embezzling funds from Libya, the new charges are a dramatic escalation — the most serious indictment a former head of state has faced in the history of France’s Fifth Republic, the governing system established in 1958.

Sarkozy denied any wrongdoing. “I learned of this new charge with the greatest stupefaction,” he said in a statement Friday. “The French must know that I am innocent of what I’m accused of. . . . I know the truth will triumph eventually.”

The specter of alleged Libyan ties clouded Sarkozy’s tenure in the Élysée Palace and has haunted him since he left the presidency after one term in 2012.

Friday’s “criminal association” charge breathes new life into the allegations that Sarkozy illegally secured millions of dollars in cash from the Gaddafi regime to fund his 2007 presidential bid.

The charges also raise new questions about Sarkozy’s motives in orchestrating the 2011 NATO operation against the Gaddafi government. Gaddafi’s regime was overthrown that year and he was captured and killed by opposition fighters.

The investigation into Sarkozy’s dealings was launched in the wake of an investigation by the French investigative outlet Mediapart in 2012.

Although the Sarkozy investigation remains ongoing, the former president will stand trial in late November on corruption charges. In what in France is known as the “eavesdropping affair,” he stands accused, along with his lawyer, of trying to illegally obtain classified information from a French judge.

Sarkozy will also stand trial in March and April 2021 on the charges of illegal campaign financing.

The former president’s legal problems extend further. In January, French magistrates also placed Thierry Gaubert, a former aide to Sarkozy, under formal investigation for criminal association.