Additional information added (first version was posted at 21:55)
The Iranian oil tanker dubbed "Haraaz" was sailing in the water of the Gulf of Aden on Monday at 22:45 p.m. local time (1905 GMT) when it was waylaid by pirates in their first night time attack against an Iranian vessel cruising in the Gulf of Aden, Mehr news agency reported on Thursday.
The vessel got away unscathed after a series of chase and escape attempts, which lasted for nearly two hours, and all the crew on board of the Iranian ship are reported to be in complete health, the report said.
It was the 31st reported attack on an Iranian vessel in the Gulf of Aden and the first such attempt in 2011, Press TV reported.
Jamal Mayahi, the technical Director of National Iranian Tanker Company, the ship is now on its way to Egypt, where it is expected to make a port call and to unload its cargo.
In July, Somali pirates failed in their previous attempt to hijack an Iranian vessel carrying crude oil to Spain en route the Bab al-Mandeb Strait in the Gulf of Aden.
The Gulf of Aden and water routes off the coast of Somalia remain the hotbed of mounting attacks on passing ships by Somali pirates in spite of the presence of some 35 international warships patrolling the lawless waters.
The Gulf of Aden is also is an important energy transit gate, particularly because of Persian Gulf oil, which is shipped to the West through the Suez Canal.
In recent years, Somali pirates have expanded the reach of their attacks, preying on merchant vessels and oil tankers in the Indian Ocean and the Gulf of Aden.