UN mission slams 'alarming' escalation of Libya violence
UNSMIL said in a statement that it was "alarmed by the continuing escalation of violence", which risked creating "new waves of displacement".
"UNSMIL notes with grave concern reports of attacks on civilians ... desecration of corpses, retribution, including looting, robberies and torching of public and private properties" in towns that Government of National Accord (GNA) forces have seized in recent days.
The statement said the allegations, if verified, "would constitute grave violations of international human rights and humanitarian law".
Libya has suffered almost a decade of conflict since longtime dictator Muammar Gaddafi was toppled and killed in a 2011 uprising backed by several Western powers.
The capture on Monday of the coastal towns of Sorman and Sabratha and smaller settlements further south was seen as a major blow to Haftar.
The current power struggle pits the UN-recognised GNA against eastern-based strongman Khalifa Haftar, who launched an offensive to seize Tripoli in April last year.
His forces rained rockets on Tripoli on Tuesday, hitting several homes around Mitiga airbase in the eastern suburbs, the capital's sole and only intermittently functioning airport.
The GNA which has been battling an offensive against the capital for just over a year, accused Haftar's forces of taking revenge against Tripoli's civilian population following their losses on Monday.
"The criminal militia and mercenaries have taken out their anger on residential neighbourhoods of Tripoli to avenge their defeat, firing dozens of rockets and missiles on the capital indiscriminately," spokesman Mohamad Gnounou said.
UNSMIL also slammed pro-Haftar forces' "indiscriminate bombardment of Tripoli", adding that rockets had landed on civilian neighbourhoods, causing casualties.
"Acts of revenge will further escalate the conflict, and lead to a cycle of revenge that threatens the social fabric in Libya," it warned.
GNA chief Fayez al-Sarraj said he would no longer negotiate a political solution with Haftar, in an interview published Wednesday by Italian daily La Repubblica.
The UN says hundreds of people have been killed and more than 200,000 displaced since Haftar launched his battle for Tripoli which quickly ground to a bloody stalemate.
Agencies contributed to this report.