The UN Security Council on Wednesday moved to impose sanctions on militias and their political supporters who are fueling Libya's escalating war.
In a resolution adopted unanimously, the 15-member council 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.
He warned of "mounting danger in Libya and beyond" given the government's "very limited capacity" to restore order and tackle the threat from heavily-armed militias.
In its resolution, the council expressed "its determination to use targeted sanctions in pursuit of stability in Libya and against those individuals and entities who threaten its stability and obstruct or undermine its successful completion of the political transition."
It singled out human rights violations, attacks on Libyan ports, foreign missions and government buildings as well as the illegal export of crude oil to support the rebels as actions that could be punished with sanctions.
The sanctions committee is due to meet next week to draw up the list of Libyans who could face an asset freeze and travel ban.
The Libyan ambassador described the resolution as a "milestone that sends a very clear message to the parties to the conflict," but said more needs to be done to bring Libya back from the brink.
British Ambassador Mark Lyall Grant, whose country holds the presidency of the Security Council, said the sanctions and the move to cut off the flow of weapons were "an important step."
"I'm not saying it's a game changer but it is a very strong political message," he said.
The council encouraged Arab countries and other nations to support an end to fighting and push the sides toward dialogue.
Asked about the Egypt-UAE airstrikes on Libya, UN spokesman Stephane Dujarric on Tuesday said the military intervention aimed at blocking the Islamist advance, if confirmed, would be unhelpful.
"We do believe that outside actors should refrain from intervening or supporting any of the armed actors involved in the fighting in Libya," he said.