UN Secretary-General Antonio Guterres said he fears Libya will end up in a "full civil war" unless moves are soon made to end the conflict, Aljazeera reports.

"Unless action is taken in the near term, it is highly likely that the current conflict will escalate into full civil war," Guterres said on Thursday in his latest report on the United Nations Support Mission in Libya.

He acknowledged the need for the support of the international community in finding a political solution for the country, where forces loyal to renegade commander Khalifa Haftar launched an offensive to take the capital Tripoli from the UN-recognised Government of National Accord (GNA) in early April.

"I urge all parties to stop using explosive weapons, including by aerial bombardment or shelling, in populated areas because of their likely indiscriminate effects," the secretary-general said.

Fighting on the outskirts of Tripoli has left 1,000 people dead and displaced more than 100,000 others since the start of Haftar's offensive.     

"A political solution to the Libyan conflict requires the full and united support of the international community," Guterres said.

"I am concerned by the presence of foreign fighters and mercenaries being employed by parties to the conflict in Libya, as well as by the influx of weapons to the country," he added, calling for strict adherence to an arms embargo in place since 2011.