The UN mission in Libya called for "immediate deescalation", citing reports of armed forces being mobilized in the capital and its surroundings that have raised fears of renewed violence.
In mid-May, there were clashes in Tripoli between forces loyal to the government and powerful armed groups wanting to dismantle it.
In a statement published late on Wednesday on X, the UN Support Mission in Libya (UNSMIL) said there were "increased reports of continued military build-up in and around Tripoli", AFP reported.
It said it "strongly urges all parties to refrain from using force, particularly in densely populated areas, and to avoid any actions or political rhetoric that could trigger escalation or lead to renewed clashes".
It called for all parties to "engage in good faith" in deescalation and for the "swift implementation of security arrangements" set out during efforts to end the May violence.
Those clashes left six people dead, the United Nations said.
"Forces recently deployed in Tripoli must withdraw without delay," UNSMIL said.
Libya has been gripped by conflict since the 2011 overthrow and killing of longtime ruler Moamer Kadhafi in a NATO-backed uprising.
The country remains split between Prime Minister Abdelhamid Dbeibah's UN-recognized government based in Tripoli and a rival administration based in the east.
In a TV interview on Monday, Dbeibah called for armed groups to vacate the areas under their control.
Among the sites held by armed factions are the Mitiga airport in the east of the capital, which is controlled by the powerful Radaa Force.
"Dialogue -- not violence -- remains the only viable path toward achieving lasting peace, stability in Tripoli and across Libya", the UNSMIL statement said.
