Pirates stormed a cargo ship off Nigeria's oil-producing southern coast, kidnapping five foreign sailors and stealing cash, a watchdog and a security source said Monday.
The International Maritime Bureau (IMB) said the April 25 incident was carried out by "14 heavily armed pirates" who boarded the vessel 45 nautical miles off the Nigerian town of Brass.
They forced their way into the ship's saferoom, making off with crew and cash, the IMB said in a statement.
A security source, who asked that his name be withheld, said those taken included three Sri Lankans, a Russian and a sailor from Myanmar.
He identified the ship as the Antigua and Barbuda-flagged MV City of Xiamen.
The Gulf of Guinea, which includes the waters off Benin, Nigeria and Togo, is an emerging piracy hub, with gunmen frequently targeting vessels believed to be carrying crude from the Niger Delta, which produces roughly 2 million barrels of oil a day.
The number of attacks in the Gulf rose from 39 in 2010, to 53 in 2011 and 62 in 2012, according to the London-based think-tank Chatham House.
Typically, foreign sailors kidnapped in such raids have been released following a ransom payment.
Three Ukrainians, two Russians and an Indian seized from a cargo ship off southern Nigeria were released in February unharmed.
Nigeria has pushed for more aggressive global action to combat piracy around the Niger Delta, and the country is looking at stepping up multi-lateral naval patrols.
Some have suggested that foreign vessels should be allowed to hire private and armed security escorts, but analysts say Nigeria is unlikely to let that proposal move forward.
Nigeria's oil industry, the eighth largest in the world, was previously crippled by an insurgency in the Delta, but a 2009 amnesty deal with oil rebels helped curb the unrest.
The current threats have so far included maritime attacks on oil ships as well as strikes against the oil-infrastructure on land.
Analysts say that poverty in the region is a key cause of the unrest.
"The toxic mix of organised crime, rising small-arms proliferation and insurgency, and high levels of youth unemployment," must be tackled to curb further attacks, Chatham House said in a report last month.
Aside from kidnappings in the Niger Delta, foreigners have also been targeted by Islamist extremist groups in the north, but that is considered a different phenomenon.
Nigeria is Africa's most populous country, roughly split between a mostly Muslim north and predominately Christian south.
Despite its considerable oil wealth, most Nigerians still live on less $2 a day, as development and poverty alleviation schemes have been held back by massive government corruption, notably in the energy sector.