Tripoli engulfed in deadly clashes between rival Libyan militias

At least 13 people have been killed in fierce clashes on Friday between rival armed groups in the Libyan capital Tripoli, seat of the country's UN-backed but largely ineffective unity government.

A security official for the Government of National Accord (GNA) separately gave a toll of 23 loyalist forces killed and 29 wounded, but medical sources were not immediately available to confirm those figures.

Tripoli has been gripped by a power struggle between dozens of militias since a NATO-backed uprising toppled longtime ruler Muammar Gaddafi in 2011.

AFP journalists heard explosions and artillery fire as fighting broke out in the Abu Slim, al-Hadhba and Salaheddin districts in the south of the city.

A militia loyal to the unity government, the Abu Slim Deterrence Force, said on its Facebook page that it lost five fighters but it was unclear if they were included in the hospital toll.

Groups hostile to the GNA said they attacked loyalist forces.

The fighting started around a complex of luxury villas that until March served as the headquarters of militias loyal to former prime minister Khalifa Ghweil.

Many of those fighters come from powerful militias in Misrata.

UN envoy Martin Kobler issued an appeal for a halt to the fighting.

"Voices of reason should prevail for the benefit of the country," he said. "Political aims must not be pursued through violence. Civilians must be protected."

British ambassador Peter Millett said on Twitter that he could hear explosions and artillery in south Tripoli.

He condemned "action by these militias who threaten security" in the run-up to the holy month of Ramadan, which begins on Saturday in Libya.

Ghweil was kicked from power when the GNA took office in March 2016 and has refused to recognise the new administration.

Loyalist forces seized the villas in four days of intense fighting in March that saw them expand their control over the capital.

On Friday, an armed Libyan group seized Al-Hadhba jail in south Tripoli where former officials of Gaddafi's government are being held, a judicial source said.

The prison guards were forced to withdraw after an armed group loyal to the UN-backed Government of National Accord attacked, said the source requesting anonymity, adding that two guards were killed.

The fate of the top former officials for Gaddafi, who was overthrown and killed in a 2011 revolution, was not known late on Friday.

More than 30 are being held there, including Gaddafi's last premier Baghdadi al-Mahmudi and his former intelligence chief, Abdullah Senussi.

Tripoli had been relatively calm since, but dozens of armed groups still operate - including several who support Ghweil.

The GNA has won the support of various militias since it took office in March last year, but several parts of Tripoli remain beyond its control. 

Relying on militia support and pitted against a rival administration in the east, the GNA has struggled to assert its authority.