A French news magazine has accused the U.S. of using Israeli spy software to hack into office of former French president Nicolas Sarkozy.

A French news magazine has accused the United States of using U.S.-Israeli spy software to hack into the office of former French president Nicolas Sarkozy during the final weeks of his presidency.

L’Express reported late Tuesday that the computers of several of Sarkozy's close advisers, including chief of staff Xavier Musca, had been compromised in May by a computer virus similar to Flame, which was allegedly created by a U.S.-Israeli team to target Iran's nuclear program.

“You can be on very good terms with a 'friendly' country and still want to guarantee their unwavering support — especially during a transition period,” an official told the magazine.

The Obama administration on Wednesday unequivocally denied reports.

“We categorically deny the allegations by unnamed sources that the U.S. government participated in a cyberattack against the French government,” Homeland Security spokesman Matthew Chandler told The Hill in a statement. “France is one of our strongest allies.

“Our outstanding cooperation in intelligence sharing, law enforcement and cyber defense has never been stronger, and remains essential in successfully combating the common threat of extremism,” Chandler added.

According to the l'Express report, however, Homeland Security Secretary Janet Napolitano reportedly did not deny the allegations when directly confronted.

“We have no greater partner than France; we have no greater ally than France,” Napolitano reportedly answered, at the opening of an interview with l'Express. “We cooperate in many security-related areas. I am here to further reinforce those ties and create new ones.”

An Obama administration official said Napolitano dismissed the question, claiming it was “preposterous.”

In the interview, Napolitano also said that the Flame and Stuxnet viruses had “never been linked to the U.S. government.”