The UN chief warned Libya is on the brink of "a very dangerous situation" as forces loyal to the internationally recognised government and a rival strongman battle for control of the capital.
Thousands of people have fled heavy fighting on the outskirts of Tripoli that has left dozens dead and prompted mounting global alarm.
UN chief Antonio Guterres on Wednesday appealed for a halt to hostilities to prevent the situation spiralling out of control.
"It's still time to stop," he told reporters after briefing the UN Security Council in a closed session in New York.
"It's still time for a ceasefire to take place, for a cessation of hostilities to take place, and to avoid the worst, which would be a dramatic, bloody battle for Tripoli."