The Paris prosecutor's office opened a preliminary investigation into a legal complaint brought by newly married French President Nicolas Sarkozy over a media report about his love life, a judicial official said Friday.

The media report, posted Wednesday on the Web site of Nouvel Observatuer news magazine, alleged Sarkozy promised to call off his engagement if his ex-wife came back to him.

Sarkozy filed a legal complaint Thursday accusing the site of having made the story up. The charges filed include "using falsehoods," and are punishable by up to three years in prison and fines of up to $65,560.

A judicial official, speaking on condition of anonymity because the case is ongoing, said a preliminary probe had begun.

The Paris-based media watchdog Reporters Without Borders expressed concern over Sarkozy's legal battle, saying the French leader's "choice of procedure alarms us."

"The president is suing the newspaper under criminal law when he could well have brought a civil suit for violation of privacy," the group said in a statement. "A criminal prosecution means the journalist targeted could be required to reveal his sources. This would not so in a civil action."

Sarkozy, 53, and model-turned-singer Carla Bruni, 40, tied the knot in a discreet ceremony in the presidential Elysee Palace before about 20 friends and family members a week ago. The wedding, his third, came just months after Nicolas and Cecilia Sarkozy ended their 11-year marriage.