Pirates have hijacked an Italian diesel tanker off Benin in western Africa in an attack of the kind more usually associated with Somalia.
Assailants boarded the RBD Anema e Core early on Sunday in the Gulf of Guinea, officials in Benin and Italy confirmed.
Two of the 23 crew are Italians, the others Filipinos and a Romanian.
Benin's navy said it was following the hijacked ship while Italy's foreign ministry liaised with its owner in Naples.
Three pirates managed to board the ship 23 nautical miles (43km) south of Cotonou, the economic capital of Benin, Italian media said.
"Everything is being done to trace the pirates as quickly as possible," Maxime Ahoyo, commander of Benin's navy, told reporters in Cotonou.
The Gulf of Guinea has become increasingly important for its potential energy reserves which have attracted international interests, BBC West Africa correspondent Thomas Fessy reports from Dakar.
The US, for example, hopes to import about a quarter of its oil supplies from the region by 2015.
West African coast guards have been receiving US training to combat growing maritime insecurity.
Most recent attacks on shipping around Africa have been off its east coast, where Somali pirates have ranged deep into the Indian Ocean, but the danger in the west was already identified several years ago.