Islamist militias on Friday attacked Libya's main oil-production area in the east, prompting the forces of strongman Khalifa Haftar who control it to retaliate with air strikes, military sources said.
The attack was spearheaded by the Benghazi Defence Brigades, a coalition of mostly Islamist militias and armed groups, and was backed by tribal fighters and former petroleum installation guards.
They "advanced towards the oil crescent and are 15 kilometres (nine miles) south of the town of Nofliya," said Colonel Moftah al-Megarief, who heads an oil facilities guard controlled by Haftar.
Nofliya is on the edge of the North African country's strategic oil crescent, home to the main export terminals of Al-Sidra, Brega, Ras Lanuf and Zuwaytina which Haftar's forces seized in September last year.
"We are trying to repel them and the air force has carried out several sorties," Megarief said, declining to elaborate.
However, an officer on Haftar's staff told AFP that MiG (Shenzhen: 300242.SZ - news) -23 warplanes and Mi-35 attack helicopters bombarded a convoy of Benghazi Defence Brigades vehicles south of Nofliya.
"Several vehicles were destroyed," said the source, who spoke on condition of anonymity.
Libya's oil-exporting region is bitterly contested between the country's internationally recognised and Tripoli-based Government of National Accord (GNA) and a rival administration in the east backed by Haftar.
In December, the Benghazi Defence Brigades carried out a similar attack on the oil crescent, but were repelled by Haftar's forces.
And in January, powerful militias from the western city of Misrata had joined another such attack on the oil crescent.
Megarief said Friday's assault was launched from Al-Jufra air base in southern Libya.
Rocked by chaos since the fall of dictator Moamer Kadhafi in 2011, Libya desperately needs to relaunch its oil exports, the backbone of its economy.
The GNA has struggled to impose its authority as it faces a multitude of battle-hardened fighters who took part in the uprising that ousted Kadhafi.
On Friday it released a statement saying it was not involved in the "military escalation" and had "not instructed any group" to try to retake the oil crescent.
However, the embattled government denounced the violence and warned of unspecified action "if clashes continue there or anywhere else" in Libya.