Pirates hijacked the St Vincent and Grenadines flagged MV Syria Star cargo vessel and its crew of 24 , said the European Union naval force.
The pirates boarded the almost 19,000 dwt ship as it was sailing west in a recommended shipping lane through the Gulf of Aden, EU Navfor said in a statement.
Helicopters and warships were sent to the scene of the hijacking but the Syria Star, which was carrying a cargo of sugar, had reversed course and was heading southeast back towards the Horn of Africa, EU Navfor said.
The pirates did not respond to attempts to contact them by radio, Reuters reports.
The crew comprises 22 Syrians and two Egyptians, the statement said.