Paris prosecutors have opened a probe into the leaking of a confidential document on planned French air strikes in Syria in 2013, which in the end were never carried out, judicial sources said Monday.

The document was obtained by two journalists from the daily Le Monde who recently published a tell-all book based on interviews with Socialist President Francois Hollande.

The investigation into possible compromising of national defence security was opened at the behest of rightwing lawmaker Eric Ciotti, the sources said.

Journalists Gerard Davet and Fabrice Lhomme wrote in Le Monde on August 30 that they had obtained a copy of a document marked "confidential" from the president.

Drafted the previous day, August 29, by Hollande's own chief of defence staff, "it detailed the timeline of the coming raid. It's the veritable handbook of French intervention," they wrote.

The article, headlined "The day Obama dropped Hollande", reported that France decided against taking part in US-led air strikes in Syria in the face of indecision by US President Barack Obama.

Defence Minister Jean-Yves Le Drian played down the leak earlier this month, saying: "What was involved? The publication in a newspaper of information... on events of three years ago and on an operation that did not take place."

France joined the international coalition fighting the Islamic State group in Iraq and Syria in September 2015.

Source: AFP