The United States has been charged with launching a cyberattack against France -- a claim the U.S. government has categorically denied.

According to L'Express, a French news outlet, sources with knowledge of a cyberattack that occurred in May have said the U.S. was behind the attack. The news outlet claims that the attack occurred a few days before the country's presidential election and targeted "the team of [former French President] Nicolas Sarkozy."

L'Express' sources say the hackers worked their way through Sarkozy's team to attack his closest advisers. In order to climb that ladder, the hackers kicked off their efforts on Facebook, identifying people who were in some way linked to Sarkozy. From there, they were sent e-mails that contained a link leading to a fake website that replicated the Elysse Palace's own page. After the page asked for a username and password, the advisers obliged, and their information was stolen.

According to L'Express, a host of important documents were obtained, including "secret notes" and Sarkozy's strategic plans.

So, why would the U.S. get involved in a cyberattack on what is one of its longest-standing allies? According to L'Express, its sources didn't say what the motive might be, but indicated that the government could have known Sarkozy would be on the way out and wanted to make friends with the incoming administration.

Government-sponsored cyberattacks are certainly nothing new. For years now, we've been hearing of reports of China and the U.S. launching cyberattacks on important networks. Claims also have been made that the U.S. and Israel were behind the Flame cyberattacks on Iran's nuclear efforts. This is the first time that there has been a report of the U.S. launching a cyberattack on an ally.

For its part, the U.S. has denied L'Express' allegations.

"We categorically refute allegations of unidentified sources, published in an article in the Express, that the government of the United States of America has participated in a cyberattack against the French government," U.S. Embassy in Paris spokesman Mitchell Moss told L'Express in a statement. "France is one of our best allies. Our cooperation is remarkable in the areas of intelligence, law enforcement, and cyber defense. It has never been so good and remains essential to achieve our common fight against extremist threats."

CNET has contacted the U.S. Department of Defense for comment on the matter. We will update this story when we have more information.

(Via The Verge)