Libya's internationally recognised government said Monday that its aircraft bombed an oil tanker off the Islamist-held port of Derna, killing two crewmen and drawing condemnation from Greece.
A spokesman for the Libyan government's armed forces said the tanker was hit on Sunday after it refused to stop for checks on its cargo which had raised suspicions.
But the Greek government said the vessel was plying a longstanding route under contract to the Libyan state oil company and demanded prosecution of those responsible for the deaths of the Greek and Romanian crewmen.
Greek coastguards said the Liberian-registered Araevo vessel was at anchor two nautical miles off Derna and laden with 1,600 tonnes of crude oil when it was hit.
Libyan armed forces spokesman Colonel Ahmed Mesmari said the tanker had turned off its lights "in preparation for entering the port... and because of this it and its cargo were considered suspicious".
But the Greek government condemned what it called a "cowardly and unprovoked" attack on a vessel plying a regular service between two Libyan ports.
"According to the shipping firm, the vessel was operating under contract to the Libyan National Corporation and had been working the Marsa al-Brega to Derna route for many years without problem," a government statement said.
"This criminal act has caused the deaths of two crew members -- one Greek and one Romanian -- and wounded two others," it said.
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"The Greek government will take all necessary steps with the Libyan authorities -- in spite of the unstable situation -- to help investigate the circumstances of this tragic event and identify and punish the attack's perpetrators."
Two other members of the ship's crew of 26 were wounded in the air strike.
Libya's internationally recognised government, which has been based in the remote east since Islamist-backed militia seized the capital last year, has been determined to prevent any oil exports without its authorisation.
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.
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.
So far the offensive has been repelled by pro-government forces, who have hit back against Libya's third largest city Misrata, which is controlled by Fajr Libya.
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.