Renewed fighting has erupted in Tripoli, leaving at least three people wounded after a barrage of rockets hit several parts of the capital, including a popular hotel.
The violence came as Britain, France, Italy and the United States warned on Saturday that an escalation would hamper the political process in Libya and plans to hold elections by December.
Witnesses told AFP news agency three people were wounded when a rocket hit the fourth floor of the Al-Waddan Hotel, which overlooks the bay of Tripoli and is located 100 metres away from the Italian embassy.
Another rocket landed on the home of a civilian family in the area of Ben Ashour. The house is about 200m from the prime minister's office.
Al Jazeera's Mahmoud Abdelwahed, reporting from Tripoli, described scenes of panic in the capital's southern suburbs, with rival militias targetting densely-populated areas.
The latest bout of fighting came a day after at least 15 rockets landed on Tripoli and its surroundings, forcing the suspension of flights in the the capital's only operational airport.
The fighting between the rival armed groups broke out earlier this week. Street battles on Monday and Tuesday pitted the Seventh Brigade, or Kaniyat, from Tarhouna, a town 65km southeast of Tripoli, against the Tripoli Revolutionaries' Brigades (TRB) and the Nawasi, two of the capital's largest factions.
The Kaniyat and other groups from outside Tripoli have noticed the success of rivals inside the city with growing unease. Reports about the wealth, power and extravagant lifestyles of some Tripoli rebel commanders have fuelled resentment.
A fragile truce took effect on Thursday, but by late afternoon the hostilities had resumed.
Libyan officials say the fighting has so far killed nearly 40 people, including 18 civilians. According to Human Rights Watch, the death toll includes at least four children.
'Attacks weaken Libyan stability'
In joint statement released by the French foreign ministry, Britain, France, Italy and the US condemned the violence, calling the "attempts to weaken the legitimate Libyan authorities" and obstruct the ongoing political process "unacceptable".
"We are calling on the armed groups to immediately stop all military action and warn those who seek to undermine stability, in Tripoli or elsewhere in Libya, that they will be made accountable for it," the statement added.
The interior Ministry of Libya's UN-backed administration, the Government of National Accord (GNA), has also denounced the renewed violence.
The GNA has blamed unnamed factions for "undermining the ceasefire ... by blindly launching rockets and shells on Tripoli and its suburbs".
Bringing armed groups to heel is seen as crucial to resolving the conflict that has divided Libya since a NATO-backed uprising removed long-time ruler Muammar Ghaddafi in 2011.
In recent years, the country has remained divided between the GNA in Tripoli and a rival administration in the east, backed by renegade General Khalifa Haftar.