Gunbattles between militiamen and armed residents have rocked the Libyan capital.
Latest reports say at least 32 people were killed and 400 wounded in the violence, the worst in Tripoli for many months.
Prime Minister Ali Zeidan demanded that all militias, "without exception," leave Tripoli.
But analysts say his government has been nearly powerless in reining in the militias.
The bloodshed began when militiamen from the city of Misurata fired at about 500 protesters demanding their eviction from the capital after they had fought rivals for control of city districts.
A Reuters reporter saw an antiaircraft cannon firing from the "Gharghur brigades'" gated compound into the crowd.
Demonstrators fled but then returned, heavily armed, to attack the compound, where the militiamen remained holed up past nightfall as fighting continued.
Based on reporting by AP and Reuters