Heavy clashes broke out in the Libyan capital Tripoli on Wednesday involving a brigade aligned with the army and a security force grouping former rebel militias that helped topple Muammar Gaddafi.
Loud explosions and gunfire could be heard coming from Tripoli's southern outskirts, where militiamen belonging to a security force known as the Supreme Security Committee (SCC) fought a brigade associated with the military.
Late on Tuesday an SSC commander was killed and four soldiers were wounded in a battle with the same brigade, led by men from the western mountain town of Zintan.
That violence had followed an attack by a different armed group from Zintan on the headquarters of a special force guarding Libyan oil facilities.
"It seems the fighting is a continuation of what happened yesterday. It could be a revenge attack for the death of the commander," a military source said.
Armed groups made up of former rebel fighters have grown in power and size nearly two years after Gaddafi was ousted and the government has struggled to impose its authority over them.
In the eastern city of Benghazi, a military intelligence officer, Lieutenant Colonel Giuma Misrati, was killed near his home when a bomb exploded in his car, officials said.