United Nations chief Antonio Guterres on Saturday called for an end to violence in Libya in accordance with a UN-brokered ceasefire agreement.
According to a health ministry toll at least 39 people have been killed and some 100 injured in five days of clashes among rival militias, which broke out Monday in suburbs south of Tripoli.
"The Secretary-General condemns the continued escalation of violence in and around Libya's capital and, in particular, the use by armed groups of indiscriminate shelling leading to the death and injury of civilians, including children," a statement from Guterres' office said.
"The Secretary-General calls on all parties to immediately cease hostilities and abide by the ceasefire agreement brokered by the United Nations and the Reconciliation Committees."
In a joint statement Britain, France, Italy and the United States have said they "warn those who tamper with security in Tripoli or elsewhere in Libya that they will be held accountable for any such actions."
Fighting continues on in Tripoli
Fighting between rival militias in Libya escalated on Saturday, with the forces of the seventh brigade seizing control of large parts of the capital Tripoli, including the airport road and a number of military camps as it continues to advance towards the city center.
In a related development, at least three people were injured in random shelling when a rocket hit the Al-Waddan Hotel, which overlooks the bay of Tripoli and is popular with foreigners, and only 100 meters away from the Italian embassy.
It was not immediately clear if they were clients or staff members.
The rival militias reached a cease-fire agreement, but continued rocket attacks breached the agreement, with more than 15 rockets hitting other parts of the city on Friday and early Saturday morning, which has been at the epicenter of a bitter power struggle since the fall of dictator Moamer Kadhafi in a 2011 NATO-backed uprising.
The country currently face a power struggle between two rival governments in Tripoli and the east of the country, each supporting a group of armed militias.