CAIRO — The Libyan national oil company declared 11 oil fields nonoperational because of “theft, looting, sabotage and destruction” by “unidentified armed groups,” the company said in a statement late Wednesday.

Libyan officials have sought to blame Islamist militants who have pledged loyalty to the Islamic State for some of the oil field attacks, including assaults last month on the Mabrouk and Bahi oil fields as well as an attack this week on the Dhahra field. That field is about 100 miles south of the coastal city of Surt, where Islamic State militants have established a foothold.

Last month, the group, also known as ISIS or ISIL, released a video that appeared to show its militants in Libya beheading a group of Egyptian Christians who had been kidnapped in Surt, raising new alarms about the group’s presence. But the group has not claimed responsibility for the oil field attacks, and other armed groups might have carried them out.