The jihadists first carried out a suicide car bomb attack on a military checkpoint at the entrance to the town of Al-Sidra, killing two soldiers, said a colonel in the army loyal to the internationally recognised government.
“We were attacked by a convoy of a dozen vehicles belonging to IS,” Bashir Boudhfira said. “They then launched an attack on the town of Ras Lanouf via the south but did not manage to enter.”
IS has been trying to push east from Sirte for several weeks to reach the country’s “oil crescent” where its main oil terminals such as Al-Sidra and Ras Lanouf are based.
A Libyan oil official told AFP that a 420,000-barrel oil tank in Ras Lanouf caught fire during the clashes.
IS on Twitter announced that its fighters had led an “attack on the Al-Sidra area followed by violent clashes with the enemies of God.”
The group said that the attack came after it took control of Ben Jawad town, 150 kilometres (90 miles) east of the central coastal city Sirte, which has been under IS control since June 2015.
No official or army source could confirm this.
Monday’s attack is the first of its kind since IS seized Sirte last summer.