In a statement after a meeting in Brussels convened by Secretary of State John Kerry, the United States, Britain, France, Germany, Italy, Spain, the European Union and the United Nations called for an immediate end to hostilities.
The ministers "expressed grave concern over the deteriorating situation in Libya" and welcomed an announcement by UN Special Representative Bernardino Leon that he will lead a new round of peace talks on December 9.
But they said that if key forces did not take part in UN-led peace moves they were willing to "consider additional measures to protect Libya's unity, stability and prosperity, and to counter expanding terrorist threats to Libya and the region".
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The statement did not give any details of what action they might take.
More than three years after dictator Moamer Kadhafi was toppled and killed in a NATO-backed revolt, Libya is awash with weapons and powerful militias, and has rival governments and parliaments.
As Washington marshalls efforts to defeat jihadists across the Middle East, there is growing concern that Libya could go the way of Syria and Iraq where the Islamic State jihadi group has seized control of large areas.
After the Libya meeting Kerry chaired the first high-level meeting of a more than 60-member US-led anti-IS coalition at NATO headquarters in Brussels.