Prime Minister Ali Zeidan is struggling to control rival militias, Islamist militants and other former fighters who refuse to surrender their arms two years after helping to overthrow Muammar Gaddafi in a NATO-backed revolt.
After Friday's violence, Zeidan demanded that all militias "without exception" leave Tripoli, but the clashes underscored how little his fledging military can do to curb ex-rebels, who have also shut down Libya's oil exports for months.
Friday's bloodshed, the worst in Tripoli for many months, began when militiamen from the city of Misrata fired at about 500 protesters demanding their eviction from the capital after they had fought rivals for control of city districts.
