The Greek coastguard has said the Liberian-flagged ARAEVO had 26 members and 12,600 tonnes of crude oil on board when it was hit by the air strike.

Two other crew members were also injured and the Greek government has demanded an investigation.

According to Reuters, the tanker's operator Athens-based Aegean Shipping Enterprises said no oil was spilled.

Aegean safety manager Elias Syrros said a war plane bombed the front part of the ship.

"There is no oil leakage, the ship's integrity was not compromised," he said.

"Damages are being assessed."

An industry source said the Libyan National Oil Company-chartered tanker was delivering oil to power generators that supply the cities of Derna, Khoms, Benghazi and Misrata.

However, military officials allied with the Libyan government said the tanker was warned not to enter port and also claimed it was transporting Islamist militants to the city of Derna.

Ahmed Bu Zayad Al-Mismari, a Libyan government spokesman, confirmed the vessel was attacked by one of its warplanes.

"The ports of Derna and Benghazi were closed, and we have cautioned all oil tankers not to get close to these ports," he said, reported by Reuters.

"Al-Mismari said the Greek vessel did let officials know its destination and did not seek permission."