UN Special Representative Bernardino Leon will lead the new round of negotiations on December 9, the organisation's Libya mission said in a statement.
It did not say where the talks would take place or who would take part.
The UN's push for dialogue came as the United States and key allies said they were ready to take further steps to protect the North African nation.
In a statement after a meeting in Brussels convened by Secretary of State John Kerry, the United States, Britain, France, Germany, Italy, Spain and the European Union "expressed grave concern over the deteriorating situation" in Libya.
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More than three years after dictator Moamer Kadhafi was toppled and killed in a NATO-backed revolt, the country is awash with weapons and powerful militias, and has rival governments and parliaments.
Fierce clashes persist in second city Benghazi and west of the capital Tripoli between forces loyal to the internationally recognised government and a rebel group of mainly Islamist militias.
A previous attempt at UN-brokered talks between the warring factions in June was unsuccessful.
But the UN mission insisted on Wednesday that a breakthrough was still possible.
"There is agreement among the various Libyan actors that the way forward is to hold an inclusive political dialogue to tackle the crisis with a view to end the fighting and alleviate the suffering of the civilian population," the UN statement said.