Misrata (Libya): IS militants briefly entered the centre of the western Libyan city of Sabratha during overnight clashes with local military brigades before retreating, local authorities said on Wednesday.
Militants have taken advantage of political chaos and a lack of central authority to establish a presence in Libya, with fighters loyal to IS seizing control in Sirte and staging attacks in several other cities.
The fighting in Sabratha started when local brigades - formerly among the many rebel groups that joined in a protest that overthrew former leader Muammar Gaddafi in 2011 - attacked suspected IS hideouts 15km (9 miles) south of the city, Sabratha's municipal council said in a statement.
It said the militants then "took advantage of the security vacuum downtown and spread out all over the city" before forced out by the brigades.
Sabratha's mayor said late on Tuesday at least four brigade fighters had been killed and five injured in the clashes.
Local media reported that as many as 17 brigade members were killed, but no officials could be reached to confirm the toll.
A security source from the western city of Zintan said on Wednesday that authorities had agreed to treat the five wounded brigade members from Sabratha, a sign that Zintan and Sabratha may be prepared to cooperate in the fight against IS.
The two cities have been on opposite sides of Libya's post-Gaddafi conflict, with Zintan allied to the internationally recognised government now based in the country's far east and Sabrathan forces among those that support a rival government whose armed supporters seized the capital Tripoli in 2014.
On Friday, the United States carried out an air strike on a suspected IS training camp in Sabratha, killing nearly 50 people. Serbia's government said two Serbian diplomats kidnapped in Libya in November also died in the attack.
Meanwhile, the French newspaper Le Monde reported on Wednesday. that French special forces and intelligence commandos are engaged in covert operations against IS militants in Libya in conjunction with the United States and Britain.
It said President Francois Hollande had authorised "unofficial military action" by both an elite armed forces unit and the covert action service of the DGSE intelligence agency in the North African state.
What Le Monde called "France's secret war in Libya" involved occasional targeted strikes against leaders of the ultra-radical group, prepared by discreet action on the ground, to try to slow its growth in Libya.
The defence ministry declined comment on the substance of Le Monde's story but a source close to Defence Minister Jean-Yves Le Drian said he had ordered an investigation into "breaches of national defence secrecy" to identify the sources of the report.
Hollande said that France was at war with IS after it claimed responsibility for a wave of attacks on 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.
It has also confirmed that France has set up an advance military base in northern Niger on the border with Libya.
Le Monde said French intelligence had initiated a strike last November that killed an Iraqi known by the nom de guerre Abu Nabil who was the senior IS 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 defence official as saying: "The last thing to do would be to intervene in Libya. We must avoid any overt military engagement, but act discreetly."