Gunmen killed at least four people, including three guards, during an attack at a French-run oil field in the desert south of the Islamist-held Libyan city of Sirte.

The al-Mabruk oil field came under attack by unknown militiamen overnight, French energy giant Total and state-run National Oil Corp (NOC) that jointly operate the site said.

"An unidentified armed group attacked the field but personnel were evacuated in time," NOC spokesman Mohamed al-Harari told AFP, dismissing early reports that a French worker was abducted.

Al-Mabruk lays some 170km (105 miles) south of Sirte, the coastal city that was the hometown of late dictator Muammar Gaddafi.

"There were no Western or French citizens. The site was subcontracted to a Libyan firm," a French diplomatic source told Reuters. "There are possibly four dead local people."

No group has claimed responsibility for the attack that came as the country is engulfed in fighting between different Islamist militia groups and pro-government forces.

Sirte has fallen in the hands of Ansar al-Sharia, a jihadi movement that recently pledged its alliance to the Islamic State (Isis) and is designated a terrorist organisation by the UN.

Last week another Islamic State-linked group calling itself the Tripoli province of the Islamic State claimed responsibility for a deadly attack on a luxury hotel in the capital of Tripoli.