* Liberia-flagged "Aegean Star" released
* All crew safe, vessel on its way to Ghana
* Pirates had seized it 12.5 miles off Benin on Saturday (Adds release, ship manager quotes)
ATHENS, July 18 (Reuters) - Pirates released a Greek-owned, Liberia-flagged tanker they had seized on Saturday 12.5 miles off the coast of Benin, and all the crew were safe, the vessel's manager said on Monday.
The 11,520 deadweight tonnage vessel Aegean Star, which was sailing from Ghana to Benin with 20 crew members, was one of two tankers captured last weekend.
Piracy is on the rise in the Gulf of Guinea, although it is not on the scale seen off Somalia, where armed sea-borne gangs are making millions of dollars in ransoms and are becoming increasingly violent.
"At approximately 2000 Greek time (1700 GMT), the pirates that had captured the oil products tanker Aegean Star left the vessel and command was resumed by the master," the managing company Aegean Bunkering Services Inc said in a statement.
The company said it was investigating whether a cargo of 8,300 metric tonnes of fuel oil and 1,500 metric tonnes of gas oil had been damaged.
The vessel was sailing to Ghana, it said.
Analysts say an increase in scope and number of attacks in a region ill-equipped to counter the threat could affect shipping and investment.
Piracy off Somalia is also of major concern. On Sunday, Somali pirates seized a United Arab Emirates owned and flagged oil tanker, the MV Jubba XX, with a crew of 16 people, the European Union's naval force said on Monday.
(Reporting by Renee Maltezou; Additional reporting by Mohamed Ahmed; Editing by Jon Boyle)
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