PARIS - French public prosecutors dropped an investigation on Thursday into a writer's accusation of attempted rape against former IMF chief Dominique Strauss-Kahn due to lack of evidence.

The Paris public prosecutor's office said evidence existed suggesting sexual assault but a prosecution on that lesser charge was not possible under the statute of limitations. The incident at the centre of the complaint dates back to 2003.

Strauss-Kahn, a Socialist who was once runaway favourite to become next French president, quit as head of the International Monetary Fund in May after police arrested him in New York on charges of attempting to rape a hotel maid. He denied the charges, which were later dropped.

In France, he was accused by writer Tristane Banon, a woman 30 years his junior, of attempted rape in a Paris flat where she went to interview him eight years ago.

While it would have been possible to launch a prosecution on a count of attempted rape, other sex assault charges fall outside the judicial time limits.

"What came to light is that, while there is not enough evidence to pursue on a count of attempted rape, there are elements that can be qualified as sexual assault," the prosecutor's office said in a statement on the outcome of a preliminary inquiry by police.  

Since the incident dated back to 2003 and Banon had only filed her complaint in 2011, the matter could not be pursued, the statement said.

Strauss-Kahn's lawyers had dismissed the accusations and launched a counter-suit against Banon for alleged defamation.

Banon's lawyer, David Koubbi, said Thursday's outcome was disappointing but proved her complaint was not a figment of her imagination.

US prosecutors decided in August to drop charges against 62-year-old Strauss-Kahn, citing concern over the credibility of the hotel maid, Nafissatou Diallo. Her lawyers have threatened to start civil proceedings.

In an emailed reaction to events in Paris, a lawyer for Diallo, Douglas Wigdor, said: "We have supported and believe that Ms Banon was sexually assaulted by Mr Strauss-Kahn and are pleased that the prosecutors in Paris, as has been reported, have found evidence supporting a sexual assault."

In a recent interview with French television, Strauss-Kahn said the nine-minute sexual encounter with Diallo that led to his arrest and a three-month legal battle was consensual. But he said: "It was a moral error and I am not proud of it."

The case abruptly ended his globe-trotting IMF career and his plans to run in next April's French presidential election. Opinion polls show that both remaining Socialist contenders for the nomination -- Francois Hollande and Martine Aubry -- are in the lead against conservative incumbent Nicolas Sarkozy.