Sources from Zillah town reported two people killed and two others missing after an attack by gunmen early on Saturday in the vicinity of Zueitina oil field checkpoint.
The sources added that the gunmen are believed to be linked to ISIS, adding that the four victims are from the Petroleum Facilities Guard staffers in Zillah town.
Zillah saw a similar attack last year by ISIS militants.
Meanwhile, the Presidential Council issued a statement condemning the attack, rendering it as terrorist and saying it is part of a series of attacks on different Libyan cities, mainly in the south.
The statement reiterates that the attack on Tripoli by Khalifa Haftar is the main reason why the security vacuum in Libya is being widened and thus exploited by terrorists and criminals.
"The attack on Tripoli will help ISIS and other terrorist groups reemerge and expand in Libya." The Presidential Council warned.
It added that the Libyan Army forces won't sit idly by and watch the terrorists wreak havoc in Libya, rather they will do all they can to continue defeating them against all odds.
Southern Libya is seeing security vacuum that has been escalated since February attack by Khalifa Haftar's forces on the region.
Ghadduwah and Al-Fuqahaa towns in the south both saw ISIS attacks, which left several people killed and injured and several houses burnt.
ISIS leader Abu Bakr Al-Baghdadi appeared last month in a video admitting the defeat of his terrorist group in Sirte, but reaffirming that ISIS remnants are still operating in southern Libya, vowing to carry out more attacks to weaken Libya's government.