Heavy clashes broke out on Monday near Ben Jawad town, east of Sirte, between IS militants and Ibrahim Jodran's armed groups, which control oil ports in central Libya.
IS militants launched their early attack and clashed with Jodran groups as they seek to control Sidra oil port and other ports in the oil crescent area. There are reports of casualties from both sides.
Sources close to Jodran armed groups say Sidra is still under control and IS attack has been repelled.
Eyewitnesses say there was a state of fear in Ras Lanuf town, 23 km east of Sidra, and some families started leaving the town.
Sidra is Libya's largest oil depots, shipping about 447,000 barrels per day. It's located some 180km to the east of Sirte, the stronghold of IS in Libya.