A Greek oil tanker hijacked by gunmen off the coast of Nigeria at the weekend has been released along with its 20-strong crew, the Greek coastguard told AFP Monday.

The Liberian-flagged oil tanker Aegean Star owned by Endeavour Marine Agency was returning to the Ghanaian port of Tema, a coastguard officer said.

"The crew are in good health," the officer said.

He added that the owners had handled the negotiations and could not give information on whether a ransom had been paid.

The ship had been hijacked on Saturday 30 nautical miles off the coast of Nigeria. It had originally set off from Ghana and was headed towards Benin.

The 20-person crew included three Greek nationals, among them the ship's captain, authorities said.

On Africa's opposite coast, pirates based in war-torn Somalia have become infamous for seizing ships in the Gulf of Aden and beyond, often demanding large ransoms in exchange for the release of the crew.

A Greek-flagged oil-laden supertanker was seized off the coast of Oman by Somali pirates in February. The vessel and crew were released in April, although the company involved did not disclose if a ransom was paid.