The air force of Libya's internationally recognised government said Monday that it carried out a deadly weekend air strike on an oil tanker in the Islamist-held eastern port of Derna.

The air force opened fire "after the crew refused to heed orders to stop for a search operation" spokesman Colonel Ahmed Mesmari said, describing the tanker as "suspicious".

Greek coastguards said a 29-year-old Greek was among two crew members of the Liberian-registered Araevo killed and that two were also wounded in Sunday's air strike. The other victim was not identified.

Mesmari said that the tanker had turned off its lights "in preparation for entering the (Derna) port... and because of this it and its cargo were considered suspicious".

According to Greek coastguards, the vessel was at anchor and laden with 1,600 tonnes of crude oil when it was hit.

Twenty-one members of the crew of 26 were Filipinos, with three Greeks and two Romanians.

The jihadist Islamic State (IS) group that has seized chunks of Iraq and Syria is thought to have gained a foothold in Derna amid the chaos in Libya since the 2011 uprising that ousted dictator Moamer Kadhafi.

More than three years after Kadhafi was toppled and killed in a NATO-backed revolt, the country remains awash with weapons and powerful militias, and has rival governments and parliaments.

In mid-December, Islamist militias in Derna announced they had formed a new coalition, ahead of an expected assault by forces of the internationally recognised government.

The newly formed Mujahedeen Shura Council, called on everyone in Derna to join the coalition.

Around the same time, the Islamist-backed Fajr Libya (Libya Dawn) militia alliance launched an offensive to try to capture Libya's main eastern oil terminals of Al-Sidra and Ras Lanuf.

But so far the offensive has been repelled by pro-government forces, who also struck Misrata, Libya's third largest city which is controlled by Fajr Libya along with the capital Tripoli.

News of the air strike came as the United Nations postponed peace talks it was hoping to hold Monday between Libya's warring factions.

The talks were originally slated for December 9 but have been repeatedly delayed due to fighting between the beleaguered internationally recognised government and Islamist-backed militias.