Clashes at a rally calling for a semi-autonomous territory to be created in eastern Libya have left one person dead in the city of Benghazi, reports say.
Witnesses said a crowd demanding a semi-autonomous region of Cyrenaica was attacked by armed men.
The plan calls for a regional parliament with control over the police but stops short of dividing Libya.
It has provoked fierce criticism from many who fear it will lead to the disintegration of the country.
Friday's violence came as hundreds of people marched to Freedom Square, Benghazi, where Ahmed Zubair al-Senussi - head of the regional council seeking a split - made a speech.
Witnesses said men armed with rifles and knives then charged into the crowd.
One protester, Bashar al-Denali, said those in the rally panicked and fled the square which was then occupied by the armed men.
Hospital officials said one person had been killed and at least five others injured, some seriously.
Benghazi militia fighters - who have been responsible for security in the city since the ousting of Muammar Gaddafi last year - chased the attackers away and restored order, witnesses said.
Last Friday, demonstrators flooded the streets of Tripoli and Benghazi to protest against federalism.
After independence in 1951, Libya's three regions - Cyrenaica, Tripolitania and Fezzan - enjoyed federal power until the country became a unitary state in 1963.
Cyrenaica in the east contains two-thirds of the country's oil reserves.
The people of Cyrenaica, known as Barqa in Arabic, felt marginalised and neglected under Col Gaddafi, who focused development on the west, correspondents say.
Benghazi was the seat of the uprising that eventually toppled the former dictator, in August last year.