Islamic State suicide attackers kill at least four at court in Libya's Misrata

At least four people were killed on Wednesday in an Islamic State group suicide bomb attack at the main court building in Libya's third-largest city Misrata, security officials said.

The officials said a suicide bomber was able to detonate an explosive vest inside the building in the centre of Misrata, a coastal city about 200 kilometres east of Tripoli.

"Three men belonging to the Islamic State organisation carried out a suicide attack against the court complex in Misrata... killing four people and wounding 15 others," a spokesman for armed forces in Misrata 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, General Mohammed Ghassri added.

Misrata is home to powerful armed forces who were the backbone of an offensive that routed IS 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 Gadaffi.

The Islamic State group said in a statement following the attack that suicide commandos had stormed a court complex in Misrata.

The extremist group remains a force in Libya despite losing control of Sirte with 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 raids on IS in Libya, killing 17 people on September 22 at a desert camp 240 kilometres southeast of Sirte.

The US Africa command said the camp was used to move extremists in and out of the country, store weapons and plot attacks.

In August, IS 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 kilometres south of Tripoli.

Haftar supports an eastern-based administration that is a rival to the GNA.