Pirates have hijacked a chemical tanker almost 900 nautical miles (1,600km) off the Horn of Africa, in waters closer to India than to Somalia.
The European Union Naval Force (Navfor) says the Hannibal II was boarded while carrying vegetable oil from Malaysia towards the Suez Canal.
The Panamanian-flagged ship has 31 crew, Navfor said.
Last month a maritime watchdog said Somali pirates had intensified attacks away from their own coast.
The International Maritime Bureau (IMB) said a strong foreign naval presence off the Somali coast had led to a drop in the number of piracy incidents there. But it said pirates were moving into larger adjacent seas.
"The master of the vessel [Hannibal II] reported that he had been attacked and boarded by pirates in an area some 860 nautical miles east of the Horn of Africa which is considerably closer to India than it is to Somalia," a Navfor statement said.
It said the crew consisted of 23 Tunisians, four Filipinos, a Croat, a Georgian, a Russian and a Moroccan.
Ship hijackings hit a five-year high in the first nine months of 2010, with Somali pirates responsible for the majority, the IMB said.
Pirates are making millions of dollars in ransoms. Earlier this month Somali pirates were reported to have received a total of $12.3m (£7.6m) for the release of two ships.
Somalia has not had an effective central government for more than 19 years and is plagued by insecurity.