In a resolution adopted unanimously, the 15-membercouncil called for an immediate ceasefire, tightened an arms embargo and asked experts to draw up a list of names of Libyans targeted for sanctions.
Libya has been sliding deeper into chaos over the past weeks, with factions now backing rival prime ministers and assemblies, while Egypt and the United Arab Emirates carried out airstrikes against Islamists.
Islamist fighters seized the Tripoli airport at the weekend, compounding the crisis in Libya that has been boiling since the fall of long-time dictator Moamer Kadhafi in 2011.
UN mission chief in Libya Tarek Mitri told the council that the clashes in recent days "have been unprecedented in their gravity and to be sure, very alarming."
Libyan Ambassador Ibrahim Dabbashi also raised alarm, saying the "situation might unravel in a full-blown civil war".
"I have always excluded the possibility of civil war but the situation has changed," he said, citing the Tripoli clashes as a new, worrisome development.
Mitri, who is wrapping up his mandate as UN envoy to Libya, said that in Tripoli, there had been unprecedented waves of Libyans fleeing fighting, with some 100,000 displaced within the country and another 150,000 fleeing abroad, including migrant workers.

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