oilfield, a security source said.
The death toll was confirmed by the National Oil Co. (NOC), which condemned the attack in a statement Saturday evening.
The attackers struck at an entrance gate to the field, which lies near the town of Zella about 760 km (470 miles) southwest of the capital, Tripoli, before fleeing, according to the source and local residents who asked not to be named.
Islamic State claimed responsibility for the attack through its Amaq news agency later Saturday.
The Zella field belongs to Zueitina Oil Co., which pumped 19,000 barrels per day on average in the last quarter of 2018 across all its fields.
An engineer told Reuters that workers at the field were safe and facilities had not been damaged.
Libya’s NOC chief said Saturday that continued instability in the country could cause it to lose 95 percent of oil production.
Speaking in Saudi Arabia ahead of a ministerial panel gathering on Sunday of top OPEC and non-OPEC producers, Mustafa Sanalla also confirmed the Zella attack.
Islamic State has been active in Libya in the turmoil since the overthrow of Moammar Gadhafi in 2011. The militant group took control of the coastal city of Sirte in 2015 but lost it late in 2016 to local forces backed by U.S. airstrikes.
In the last two years, the group has targeted three state institutions in Tripoli, home of the U.N.-backed government of national accord led by Prime Minister Fayez al-Serraj.
Saturday’s assault took place as Khalifa Haftar’s Libyan National Army, which is allied to a rival administration in eastern Libya, mounts an offensive to control Tripoli.