Islamist militias launched an air strike near key oil terminals in eastern Libya on Tuesday, stepping up a battle for the government-held facilities, a security official said.

It was the first time that Fajr Libya, a coalition of Islamist militias, has carried out an air raid on the oil region of Al-Hilal, which is home to the Al-Sidra, Ras Lanuf and Brega terminals.

Ali al-Hassi, security spokesman for the region, told AFP that a warplane fired missiles at a sector to the west of Al-Sidra, without causing casualties or damage.

Anti-aircraft fire repelled the plane, which the official said could have been planning to target army fighters and helicopters parked on a nearby landing strip operated by Ras Lanuf oil company.

The air force sent reinforcements on Monday to defend the country's vital Al-Hilal facilities.

Jets and helicopters over the weekend repelled advancing Islamist fighters, who also clashed on the ground with pro-government forces. No casualty figures were available from the fighting.

In Tripoli, a car bomb on Tuesday exploded near the capital's security headquarters, without causing casualties, a security source said, declining to be identified.

Cars and buildings were damaged in the blast.

More than three years after dictator Moamer Kadhafi was toppled and killed in a NATO-backed revolt, Libya is still awash with weapons and powerful militias, and has rival parliaments as well as governments.

Islamists have seized Tripoli and Benghazi in the east, and forces loyal to internationally recognised Prime Minister Abdullah al-Thani are fighting to regain control of the cities.

The United Nations Support Mission in Libya on Tuesday condemned the military escalation in Al-Hilal and called for an immediate ceasefire "to give the Libyan political dialogue a chance".

"The Libyan oil belongs to the Libyan people and should not be manipulated by any group," it said.

"The latest military escalation is evidence that dialogue to reach a consensus is all too necessary and should be pursued with stronger determination."

A first meeting of members of the rival parliaments in Libya took place at the end of September but without producing results.

On the economic front, National Oil Company spokesman Mohamed al-Harari said oil production has slumped with the Al-Sidra and Ras Lanuf ports closed because of the fighting.

According to industry experts, output is running at around 250,000 barrels per day compared to 800,000 bpd before the latest violence.

On another battlefront, government forces and Fajr Libya militiamen resumed fighting Tuesday in the west of the country near Ras Jedir border post with Tunisia, security sources said.

Seventeen militiamen were killed in an air strike by pro-government forces in the area on Sunday.