At least eight people died in the clashes on Thursday and Friday, Libyan news agency LANA has reported.

A resident of Tripoli told the AP news agency that civilians had locked themselves up at home.

"We haven't slept all night and we haven't left the house since yesterday. All we are hearing is screaming, bombings and gunfire," she said, adding that the situation was "going from bad to worse."

Various militias carved up Tripoli after the ouster of Moammar Gadhafi in 2011, with violence dying down in recent years and the groups largely maintaining the so-called "balance of terror." A number of groups support the UN-backed unity government that was formed earlier this year, with ultraconservative "Rada" militia and the powerful Tripoli Revolutionaries backing the nascent administration. Others, including hardliners loyal to Grand Mufti Sadek al-Ghariani and fighters supporting one-time jihadist commander Abdel-Hakim Belhaj, remain skeptical.

Back to RPGs and tanks

The two sides have been trading accusations of killings and kidnappings, but the exact cause of for the latest outbreak of violence was not immediately clear.

"This is a struggle over power. Each of the warring parties has its political and ideological agendas," said Sami al-Atrash, a Tripoli resident and a legal expert. "The clashes are belated. They were expected at any moment and finally happened." he added.

On Thursday night, the Rada and the Tripoli Revolutionaries seized the five-star Al Mahary Radisson Blu Hotel where commander Belhaj previously turned some of the rooms to his offices. They also took over a barracks occupied by their rivals. Fighting also broke out in several other neighborhoods, and a witness reported a major road was blocked off by shipping containers.

Other eyewitness reported militiamen firing RPGs from the rooftops, and armored vehicles and pick-up trucks with mounted machine guns roaming the streets. According to unverified videos, one of the factions bulldozed a camp belonging to another overnight.

Violence across Libya

None of Libya's three competing administrations has managed to put the militia's under control. The unity government, led by Fayez Sarraj, called for restraint and condemned the clashes in a statement on Friday.

Although Tripoli has been relatively calm since an Islamist coalition seized its international airport in 2014, fighting has been raging in other parts of the country.  Khalifa Haftar, the general loyal to the Tobruk-based government, is fighting militants in Benghazi while the forces of the unity government are trying to drive out the "Islamic State" from the city of Sirte.

 dj/msh (AP, dpa, Reuters)