French special forces and intelligence commandos are engaged in covert operations against Islamic State militants in Libya in conjunction with the United States and Britain, the French newspaper Le Monde reported on Wednesday.
It said President Francois Hollande had authorized "unofficial military action" by both an elite armed forces unit and the covert action service of the DGSE intelligence agency in the conflict-ridden North African state, which has two rival governments and largely ungoverned desert spaces.
What Le Monde called "France's secret war in Libya" involved occasional targeted strikes against leaders of the ultra-radical Islamist group, prepared by discreet action on the ground, to try to slow its growth in Libya.
The defense ministry declined comment on the substance of Le Monde's story but a source close to Defense Minister Jean-Yves Le Drian said he had ordered an investigation into "breaches of national defense secrecy" to identify the sources of the report.
Hollande said that France was at war with Islamic State after it claimed responsibility for a wave of attacks on bars, restaurants, a concert hall and the national soccer stadium in Paris on November 13 last year, killing 130 people.
The ministry has previously confirmed that French aircraft recently conducted reconnaissance flights over Libya, where France took a leading role in a 2011 NATO air campaign that helped rebels overthrow Muammar Gaddafi's autocratic rule.
It has also confirmed that France has set up an advance military base in northern Niger on the border with Libya.
U.S. warplanes struck an Islamic State training camp in Libya last Friday in attacks that killed nearly 50 people including two Serbian embassy employees abducted last November, according to Serbia's prime minister.
U.S. officials said the site in Sabratha, western Libya, was used by up to 60 militants, including Tunisian Noureddine Chouchane, blamed for two attacks on tourists in Tunisia last year in which dozens were killed.
Le Monde said French intelligence had initiated a previous strike last November that killed an Iraqi known by the nom de guerre Abu Nabil who was the senior Islamic State leader in Libya at the time.
Le Monde said specialist bloggers had reported sightings of French special forces in eastern Libya since mid-February. It quoted a senior French defense official as saying: "The last thing to do would be to intervene in Libya. We must avoid any overt military engagement, but act discreetly."