The officials said a suicide bomber was able to detonate an explosive vest inside the building in the center of Misrata, a coastal city about 200 km east of Tripoli.
Three men belonging to Daesh “carried out a suicide attack against the court complex in Misrata... killing four people and wounding 15 others,” Gen. Mohammed Ghassri, a spokesman for armed forces in Misrata that are loyal to the country’s internationally backed government, told AFP.
He said the three men got out of a vehicle and one was able to push his way into the building and set off explosives. Of the other two, one was shot dead and the other arrested, Ghassri said.
Misrata is home to powerful armed forces who were the backbone of an offensive that routed Daesh from the coastal city of Sirte in December 2016.
That offensive was backed by Libya’s UN-endorsed Government of National Accord (GNA), one of two main rival governments that emerged from the chaos that followed the 2011 ouster of long-time strongman Muammar Qaddafi.
There was no immediate claim of responsibility from Daesh for Wednesday’s attack, but the militant group remains a force in Libya despite losing control of Sirte.
Many of its fighters have redeployed to the country’s vast and lawless desert south.
The US military last month carried out a wave of air strikes on Daesh in Libya, killing 17 people on Sept. 22 at a desert camp 240 km southeast of Sirte.
The US Africa command said the camp was used to move militants in and out of the country, store weapons and plot attacks.
In August, Daesh claimed responsibility for an attack in which 11 people were beheaded at a checkpoint manned by forces loyal to military strongman Khalifa Haftar.
Nine soldiers and two civilians were killed in that attack in the Al-Jufra region about 500 km south of Tripoli.
Haftar supports an eastern-based administration that is a rival to the GNA.