Be ready for Libya military intervention, says France

French Foreign Minister Jean-Marc Ayrault on Friday urged the international community to prepare to help Libya's unity government if asked, providing military support if necessary.

The country's UN-backed unity government is trying to assert its authority in Tripoli, but the sudden arrival of a new prime minister-designate has drawn fury from the unrecognised body in charge of the capital.

"Libya is a concern shared by all the countries of the region and beyond," Ayrault said in comments to a French newspaper.

"The chaos which reigns there today aids the rapid development of terrorism. It is a direct threat to the region and to Europe," he said.

While Islamic State group militants are being pushed back in Syria and Iraq with the help of international intervention, the extremists are gaining ground in Libya, the foreign minister warned.

"We must be prepared to respond if the national unity government of (prime minister-designate Fayez) al-Sarraj asks for help, including on the military front," he said.

Asked specifically on the likelihood of military intervention, Ayrault replied: "That will depend on the legal government. To think of launching airstrikes outside of the political process is not an option."

Libya's unrecognised authorities in control of Tripoli on Wednesday demanded that the head of a UN-backed unity government, Fayez al-Sarraj, leave - just hours after he arrived in the capital.

In a televised address, the head of the Tripoli authorities, Khalifa Ghweil, said Sarraj's government was "illegal", asking him to leave the capital or to "hand himself in".

Ayrault cautioned that the international community must avoid the mistakes of the past, citing military intervention in Iraq.

"That upset the region and brought about extremism and [IS]," he said.

Libya has had two rival administrations since mid-2014, when the militia alliance overran Tripoli, setting up its own authority and forcing the internationally recognised parliament to flee to the country's remote east.

International leaders, increasingly alarmed by the rise of extremists and people-smugglers in the North African state, have called on Libya's political rivals to back the unity government.

The United States and its European allies have threatened action against those who undermine the political process.

Meanwhile, ten Libyan cities that had been under control of the non-recognised government of Tripoli have broken away and pledged their support to the UN-backed government, one of the municipalities announced online.

The news is a major blow to the unrecognised authority in Tripoli that is refusing to give up power.

The announcement came in a statement on the official Facebook page of the Sabratha municipality on Thursday, after a meeting between representatives from the 10 coastal cities in the west of Libya located between Tripoli and the border with Tunisia.

The statement called on all Libyans to "support the national unity government" and welcomed the arrival of prime minister-designate Fayez al-Sarraj along with several members of his cabinet to the capital.

The group also asked the internationally recognised government to "put an immediate end to all armed conflicts across Libya".