At least four people were killed and 33 wounded when two car bombs exploded at a funeral for a former special forces commander in the eastern Libyan city of Benghazi.

Those killed in Thursday's blast included two civilians and two soldiers, while soldiers, police, and civilians were among the injured, Interior Ministry spokesman Tarek el-Kharraz told The Associated Press.

Several senior Libya National Army (LNA) figures, including current head of the special forces Wanis Bukhamada, attended the funeral service when the explosions happened, but none of the military leaders was killed or wounded, Kharraz said.

Al Jazeera's Mahmoud Abdelwahed, reporting from the capital, Tripoli, quoted medical sources in Benghazi as saying the death toll could rise, with many of those wounded in critical condition.

Colonel Khalifa Alobiedi, a military engineer who was at the bomb site, said initial findings suggested the attack was caused by two bomb-laden cars. He pointed to two burned vehicles about 10 metres apart.

No immediate claim of responsibility was made.

Renegade commander Khalifa Haftar leads the LNA, which is aligned with an eastern-based government. 

Shortly after the explosions, Haftar ordered an investigation into the attack.

According to Kharraz, the east-based government recently arrested a group of collaborators inside Benghazi who were in touch with Tripoli-based militias. During interrogation, they confessed there were other cells of collaborators inside the LNA stronghold.

Haftar's forces have been fighting rival militias since April in a bid to wrestle control of Tripoli from Libya's internationally recognised Government of National Accord (GNA).

Fighting has killed more than 1,000 people since it erupted, according to the United Nations, including at least 106 civilians.

UN urges ceasefire

The UN Security Council last week called on Libya's warring parties to commit to a ceasefire after a deadly air raid on a detention centre for migrants and refugees near Tripoli killed at least 60 people and wounded 77 others.

GNA blamed Haftar's forces for the attack, which UN officials said "could constitute a war crime".

LNA denied the accusations, however, saying it targeted a nearby militia's position but did not attack a hangar where the migrants were being held.

Libya is one of the main departure points for African migrants and refugees fleeing poverty and war to reach Europe by boat, but many are intercepted at sea and brought back by the Libyan coastguard - with the approval of the European Union.

An estimated 6,000 migrants and refugees are held in detention centres across the sprawling North African country, despite the UN repeatedly warning it is not safe and calling for their release.

Oil-rich and home to vast swaths of largely unpopulated desert, Libya splintered into a patchwork of competing power bases following the overthrow of former leader Muammar Gaddafi in 2011.

LNA, which holds the country's east and much of the south, enjoys the support of Egypt, the United Arab Emirates, and Russia.

But it has faced stiff resistance from fighters aligned with the GNA, which is aided by Turkey and Qatar.

Haftar, who casts himself as a foe of "extremism" but is viewed by opponents as a new authoritarian leader in the mould of Gaddafi, has previously vowed to continue his offensive until Libya is "cleansed" of "terrorism".